diff --git a/src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeCustomAttributeData.cs b/src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeCustomAttributeData.cs
index bd3134aa1c1752..adda9e7ca4f3f9 100644
--- a/src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeCustomAttributeData.cs
+++ b/src/coreclr/System.Private.CoreLib/src/System/Reflection/RuntimeCustomAttributeData.cs
@@ -18,7 +18,7 @@ internal static IList<CustomAttributeData> GetCustomAttributesInternal(RuntimeTy
             Debug.Assert(target is not null);
 
             IList<CustomAttributeData> cad = GetCustomAttributes(target.GetRuntimeModule(), target.MetadataToken);
-            RuntimeType.ListBuilder<Attribute> pcas = default;
+            ListBuilder<Attribute> pcas = default;
             PseudoCustomAttribute.GetCustomAttributes(target, (RuntimeType)typeof(object), ref pcas);
             return pcas.Count > 0 ? GetCombinedList(cad, ref pcas) : cad;
         }
@@ -28,7 +28,7 @@ internal static IList<CustomAttributeData> GetCustomAttributesInternal(RuntimeFi
             Debug.Assert(target is not null);
 
             IList<CustomAttributeData> cad = GetCustomAttributes(target.GetRuntimeModule(), target.MetadataToken);
-            RuntimeType.ListBuilder<Attribute> pcas = default;
+            ListBuilder<Attribute> pcas = default;
             PseudoCustomAttribute.GetCustomAttributes(target, (RuntimeType)typeof(object), ref pcas);
             return pcas.Count > 0 ? GetCombinedList(cad, ref pcas) : cad;
         }
@@ -38,7 +38,7 @@ internal static IList<CustomAttributeData> GetCustomAttributesInternal(RuntimeMe
             Debug.Assert(target is not null);
 
             IList<CustomAttributeData> cad = GetCustomAttributes(target.GetRuntimeModule(), target.MetadataToken);
-            RuntimeType.ListBuilder<Attribute> pcas = default;
+            ListBuilder<Attribute> pcas = default;
             PseudoCustomAttribute.GetCustomAttributes(target, (RuntimeType)typeof(object), ref pcas);
             return pcas.Count > 0 ? GetCombinedList(cad, ref pcas) : cad;
         }
@@ -87,13 +87,13 @@ internal static IList<CustomAttributeData> GetCustomAttributesInternal(RuntimePa
         {
             Debug.Assert(target is not null);
 
-            RuntimeType.ListBuilder<Attribute> pcas = default;
+            ListBuilder<Attribute> pcas = default;
             IList<CustomAttributeData> cad = GetCustomAttributes(target.GetRuntimeModule()!, target.MetadataToken);
             PseudoCustomAttribute.GetCustomAttributes(target, (RuntimeType)typeof(object), ref pcas);
             return pcas.Count > 0 ? GetCombinedList(cad, ref pcas) : cad;
         }
 
-        private static ReadOnlyCollection<CustomAttributeData> GetCombinedList(IList<CustomAttributeData> customAttributes, ref RuntimeType.ListBuilder<Attribute> pseudoAttributes)
+        private static ReadOnlyCollection<CustomAttributeData> GetCombinedList(IList<CustomAttributeData> customAttributes, ref ListBuilder<Attribute> pseudoAttributes)
         {
             Debug.Assert(pseudoAttributes.Count != 0);
 
@@ -922,7 +922,7 @@ internal static object[] GetCustomAttributes(RuntimeType type, RuntimeType caTyp
             if (type.IsGenericType && !type.IsGenericTypeDefinition)
                 type = (type.GetGenericTypeDefinition() as RuntimeType)!;
 
-            RuntimeType.ListBuilder<Attribute> pcas = default;
+            ListBuilder<Attribute> pcas = default;
             PseudoCustomAttribute.GetCustomAttributes(type, caType, ref pcas);
 
             // if we are asked to go up the hierarchy chain we have to do it now and regardless of the
@@ -935,7 +935,7 @@ internal static object[] GetCustomAttributes(RuntimeType type, RuntimeType caTyp
                 return attributes;
             }
 
-            RuntimeType.ListBuilder<object> result = default;
+            ListBuilder<object> result = default;
             bool mustBeInheritable = false;
 
             for (int i = 0; i < pcas.Count; i++)
@@ -964,7 +964,7 @@ internal static object[] GetCustomAttributes(RuntimeMethodInfo method, RuntimeTy
             if (method.IsGenericMethod && !method.IsGenericMethodDefinition)
                 method = (method.GetGenericMethodDefinition() as RuntimeMethodInfo)!;
 
-            RuntimeType.ListBuilder<Attribute> pcas = default;
+            ListBuilder<Attribute> pcas = default;
             PseudoCustomAttribute.GetCustomAttributes(method, caType, ref pcas);
 
             // if we are asked to go up the hierarchy chain we have to do it now and regardless of the
@@ -977,7 +977,7 @@ internal static object[] GetCustomAttributes(RuntimeMethodInfo method, RuntimeTy
                 return attributes;
             }
 
-            RuntimeType.ListBuilder<object> result = default;
+            ListBuilder<object> result = default;
             bool mustBeInheritable = false;
 
             for (int i = 0; i < pcas.Count; i++)
@@ -1033,7 +1033,7 @@ internal static object[] GetCustomAttributes(RuntimeFieldInfo field, RuntimeType
             Debug.Assert(field is not null);
             Debug.Assert(caType is not null);
 
-            RuntimeType.ListBuilder<Attribute> pcas = default;
+            ListBuilder<Attribute> pcas = default;
             PseudoCustomAttribute.GetCustomAttributes(field, caType, ref pcas);
             object[] attributes = GetCustomAttributes(field.GetRuntimeModule(), field.MetadataToken, pcas.Count, caType);
             if (pcas.Count > 0) pcas.CopyTo(attributes, attributes.Length - pcas.Count);
@@ -1045,7 +1045,7 @@ internal static object[] GetCustomAttributes(RuntimeParameterInfo parameter, Run
             Debug.Assert(parameter is not null);
             Debug.Assert(caType is not null);
 
-            RuntimeType.ListBuilder<Attribute> pcas = default;
+            ListBuilder<Attribute> pcas = default;
             PseudoCustomAttribute.GetCustomAttributes(parameter, caType, ref pcas);
             object[] attributes = GetCustomAttributes(parameter.GetRuntimeModule()!, parameter.MetadataToken, pcas.Count, caType);
             if (pcas.Count > 0) pcas.CopyTo(attributes, attributes.Length - pcas.Count);
@@ -1101,7 +1101,7 @@ private static bool IsCustomAttributeDefined(
             {
                 Debug.Assert(attributeCtorToken == 0);
 
-                RuntimeType.ListBuilder<object> derivedAttributes = default;
+                ListBuilder<object> derivedAttributes = default;
 
                 for (int i = 0; i < attributeTokens.Length; i++)
                 {
@@ -1139,7 +1139,7 @@ private static bool IsCustomAttributeDefined(
         private static object[] GetCustomAttributes(
             RuntimeModule decoratedModule, int decoratedMetadataToken, int pcaCount, RuntimeType attributeFilterType)
         {
-            RuntimeType.ListBuilder<object> attributes = default;
+            ListBuilder<object> attributes = default;
 
             AddCustomAttributes(ref attributes, decoratedModule, decoratedMetadataToken, attributeFilterType, false, default);
 
@@ -1156,11 +1156,11 @@ private static object[] GetCustomAttributes(
                             "attribute instantiation which is present in the code linker has analyzed." +
                             "As such the reflection usage in this method will never fail as those methods/fields will be present.")]
         private static void AddCustomAttributes(
-            ref RuntimeType.ListBuilder<object> attributes,
+            ref ListBuilder<object> attributes,
             RuntimeModule decoratedModule, int decoratedMetadataToken,
             RuntimeType? attributeFilterType, bool mustBeInheritable,
             // The derivedAttributes list must be passed by value so that it is not modified with the discovered attributes
-            RuntimeType.ListBuilder<object> derivedAttributes)
+            ListBuilder<object> derivedAttributes)
         {
             CustomAttributeRecord[] car = RuntimeCustomAttributeData.GetCustomAttributeRecords(decoratedModule, decoratedMetadataToken);
 
@@ -1295,7 +1295,7 @@ private static bool FilterCustomAttributeRecord(
             MetadataToken decoratedToken,
             RuntimeType attributeFilterType,
             bool mustBeInheritable,
-            ref RuntimeType.ListBuilder<object> derivedAttributes,
+            ref ListBuilder<object> derivedAttributes,
             out RuntimeType attributeType,
             out IRuntimeMethodInfo? ctorWithParameters,
             out bool isVarArg)
@@ -1409,7 +1409,7 @@ private static bool MatchesTypeFilter(RuntimeType attributeType, RuntimeType att
 
         #region Private Static Methods
         private static bool AttributeUsageCheck(
-            RuntimeType attributeType, bool mustBeInheritable, ref RuntimeType.ListBuilder<object> derivedAttributes)
+            RuntimeType attributeType, bool mustBeInheritable, ref ListBuilder<object> derivedAttributes)
         {
             AttributeUsageAttribute? attributeUsageAttribute = null;
 
@@ -1595,7 +1595,7 @@ private static void VerifyPseudoCustomAttribute(RuntimeType pca)
         #endregion
 
         #region Internal Static
-        internal static void GetCustomAttributes(RuntimeType type, RuntimeType caType, ref RuntimeType.ListBuilder<Attribute> pcas)
+        internal static void GetCustomAttributes(RuntimeType type, RuntimeType caType, ref ListBuilder<Attribute> pcas)
         {
             Debug.Assert(type is not null);
             Debug.Assert(caType is not null);
@@ -1639,7 +1639,7 @@ internal static bool IsDefined(RuntimeType type, RuntimeType? caType)
             return false;
         }
 
-        internal static void GetCustomAttributes(RuntimeMethodInfo method, RuntimeType caType, ref RuntimeType.ListBuilder<Attribute> pcas)
+        internal static void GetCustomAttributes(RuntimeMethodInfo method, RuntimeType caType, ref ListBuilder<Attribute> pcas)
         {
             Debug.Assert(method is not null);
             Debug.Assert(caType is not null);
@@ -1679,7 +1679,7 @@ internal static bool IsDefined(RuntimeMethodInfo method, RuntimeType? caType)
             return false;
         }
 
-        internal static void GetCustomAttributes(RuntimeParameterInfo parameter, RuntimeType caType, ref RuntimeType.ListBuilder<Attribute> pcas)
+        internal static void GetCustomAttributes(RuntimeParameterInfo parameter, RuntimeType caType, ref ListBuilder<Attribute> pcas)
         {
             Debug.Assert(parameter is not null);
             Debug.Assert(caType is not null);
@@ -1735,7 +1735,7 @@ internal static bool IsDefined(RuntimeParameterInfo parameter, RuntimeType? caTy
             return false;
         }
 
-        internal static void GetCustomAttributes(RuntimeFieldInfo field, RuntimeType caType, ref RuntimeType.ListBuilder<Attribute> pcas)
+        internal static void GetCustomAttributes(RuntimeFieldInfo field, RuntimeType caType, ref ListBuilder<Attribute> pcas)
         {
             Debug.Assert(field is not null);
             Debug.Assert(caType is not null);
diff --git a/src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs b/src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs
index e9fddd436b3d34..a76d750184af87 100644
--- a/src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs
+++ b/src/coreclr/System.Private.CoreLib/src/System/RuntimeType.CoreCLR.cs
@@ -53,87 +53,6 @@ internal enum MemberListType
             HandleToInfo
         }
 
-        // Helper to build lists of MemberInfos. Special cased to avoid allocations for lists of one element.
-        internal struct ListBuilder<T> where T : class
-        {
-            private T[]? _items;
-            private T _item;
-            private int _count;
-            private int _capacity;
-
-            public ListBuilder(int capacity)
-            {
-                _items = null;
-                _item = null!;
-                _count = 0;
-                _capacity = capacity;
-            }
-
-            public T this[int index]
-            {
-                get
-                {
-                    Debug.Assert(index < Count);
-                    return (_items != null) ? _items[index] : _item;
-                }
-            }
-
-            public T[] ToArray()
-            {
-                if (_count == 0)
-                    return Array.Empty<T>();
-                if (_count == 1)
-                    return new T[1] { _item };
-
-                Array.Resize(ref _items, _count);
-                _capacity = _count;
-                return _items!;
-            }
-
-            public void CopyTo(object[] array, int index)
-            {
-                if (_count == 0)
-                    return;
-
-                if (_count == 1)
-                {
-                    array[index] = _item;
-                    return;
-                }
-
-                Array.Copy(_items!, 0, array, index, _count);
-            }
-
-            public int Count => _count;
-
-            public void Add(T item)
-            {
-                if (_count == 0)
-                {
-                    _item = item;
-                }
-                else
-                {
-                    if (_count == 1)
-                    {
-                        if (_capacity < 2)
-                            _capacity = 4;
-                        _items = new T[_capacity];
-                        _items[0] = _item;
-                    }
-                    else if (_capacity == _count)
-                    {
-                        int newCapacity = 2 * _capacity;
-                        Array.Resize(ref _items, newCapacity);
-                        _capacity = newCapacity;
-                    }
-
-                    _items![_count] = item;
-                }
-                _count++;
-            }
-        }
-
         internal sealed class RuntimeTypeCache
         {
             private const int MAXNAMELEN = 1024;
@@ -2826,7 +2745,7 @@ public override InterfaceMapping GetInterfaceMap([DynamicallyAccessedMembers(Dyn
                     }
 
                     // All the methods have the exact same name and sig so return the most derived one.
-                    return System.DefaultBinder.FindMostDerivedNewSlotMeth(candidates.ToArray(), candidates.Count) as MethodInfo;
+                    return System.DefaultBinder.FindMostDerivedNewSlotMeth(candidates.AsSpan());
                 }
             }
 
@@ -2855,7 +2774,7 @@ public override InterfaceMapping GetInterfaceMap([DynamicallyAccessedMembers(Dyn
             }
 
             if ((bindingAttr & BindingFlags.ExactBinding) != 0)
-                return System.DefaultBinder.ExactBinding(candidates.ToArray(), types) as ConstructorInfo;
+                return System.DefaultBinder.ExactBinding(candidates.AsSpan(), types);
 
             binder ??= DefaultBinder;
             return binder.SelectMethod(bindingAttr, candidates.ToArray(), types, modifiers) as ConstructorInfo;
@@ -2893,7 +2812,7 @@ public override InterfaceMapping GetInterfaceMap([DynamicallyAccessedMembers(Dyn
             }
 
             if ((bindingAttr & BindingFlags.ExactBinding) != 0)
-                return System.DefaultBinder.ExactPropertyBinding(candidates.ToArray(), returnType, types);
+                return System.DefaultBinder.ExactPropertyBinding(candidates.AsSpan(), returnType, types);
 
             binder ??= DefaultBinder;
             return binder.SelectProperty(bindingAttr, candidates.ToArray(), returnType, types, modifiers);
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj b/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
index 8f45dd1a4d5b92..b55bda48bb1e22 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj
@@ -416,7 +416,6 @@
     <Compile Include="System\Reflection\Runtime\General\Helpers.cs" />
     <Compile Include="System\Reflection\Runtime\General\IRuntimeMemberInfoWithNoMetadataDefinition.cs" />
     <Compile Include="System\Reflection\Runtime\General\LegacyCustomAttributeApis.cs" />
-    <Compile Include="System\Reflection\Runtime\General\ListBuilder.cs" />
     <Compile Include="System\Reflection\Runtime\General\MetadataReaderExtensions.cs" />
     <Compile Include="System\Reflection\Runtime\General\MetadataReaderExtensions.NativeFormat.cs" />
     <Compile Include="System\Reflection\Runtime\General\NamespaceChain.cs" />
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeTypeInfo.BindingFlags.cs b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeTypeInfo.BindingFlags.cs
index bee3e2f9d1aad5..4725a332e17b03 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeTypeInfo.BindingFlags.cs
+++ b/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/TypeInfos/RuntimeTypeInfo.BindingFlags.cs
@@ -38,7 +38,7 @@ protected sealed override ConstructorInfo GetConstructorImpl(BindingFlags bindin
             }
 
             if ((bindingAttr & BindingFlags.ExactBinding) != 0)
-                return System.DefaultBinder.ExactBinding(candidates.ToArray(), types) as ConstructorInfo;
+                return System.DefaultBinder.ExactBinding(candidates.AsSpan(), types);
 
             binder ??= DefaultBinder;
 
diff --git a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
index 2b774a2f4fd550..32761e742f1726 100644
--- a/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
+++ b/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems
@@ -707,6 +707,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\InvokeUtils.cs" Condition="'$(FeatureNativeAot)' != 'true'" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\IReflect.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\IReflectableType.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\ListBuilder.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\LocalVariableInfo.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\ManifestResourceInfo.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Reflection\MemberFilter.cs" />
@@ -2719,4 +2720,4 @@
     <Compile Include="$(MSBuildThisFileDirectory)System\Numerics\IUnaryPlusOperators.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)System\Numerics\IUnsignedNumber.cs" />
   </ItemGroup>
-</Project>
+</Project>
\ No newline at end of file
diff --git a/src/libraries/System.Private.CoreLib/src/System/DefaultBinder.cs b/src/libraries/System.Private.CoreLib/src/System/DefaultBinder.cs
index 3adad0979c6ebf..c60123dc1e2f32 100644
--- a/src/libraries/System.Private.CoreLib/src/System/DefaultBinder.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/DefaultBinder.cs
@@ -3,9 +3,10 @@
 
 #pragma warning disable CA1852 // DefaultBinder is derived from in some targets
 
-using System.Reflection;
+using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
+using System.Reflection;
 using System.Runtime.InteropServices;
 using CultureInfo = System.Globalization.CultureInfo;
 
@@ -788,12 +789,10 @@ public sealed override void ReorderArgumentArray(ref object?[] args, object stat
 
         // Return any exact bindings that may exist. (This method is not defined on the
         //  Binder and is used by RuntimeType.)
-        public static MethodBase? ExactBinding(MethodBase[] match, Type[] types)
+        public static T? ExactBinding<T>(ReadOnlySpan<T> match, Type[] types) where T : MethodBase
         {
-            ArgumentNullException.ThrowIfNull(match);
-
-            MethodBase[] aExactMatches = new MethodBase[match.Length];
-            int cExactMatches = 0;
+            T singleMatch = default!;
+            using ValueListBuilder<T> exactMatches = new(new Span<T>(ref singleMatch));
 
             for (int i = 0; i < match.Length; i++)
             {
@@ -802,6 +801,7 @@ public sealed override void ReorderArgumentArray(ref object?[] args, object stat
                 {
                     continue;
                 }
+
                 int j;
                 for (j = 0; j < types.Length; j++)
                 {
@@ -811,29 +811,27 @@ public sealed override void ReorderArgumentArray(ref object?[] args, object stat
                     if (!pCls.Equals(types[j]))
                         break;
                 }
+
                 if (j < types.Length)
                     continue;
 
                 // Add the exact match to the array of exact matches.
-                aExactMatches[cExactMatches] = match[i];
-                cExactMatches++;
+                exactMatches.Append(match[i]);
             }
 
-            if (cExactMatches == 0)
+            if (exactMatches.Length == 0)
                 return null;
 
-            if (cExactMatches == 1)
-                return aExactMatches[0];
+            if (exactMatches.Length == 1)
+                return exactMatches[0];
 
-            return FindMostDerivedNewSlotMeth(aExactMatches, cExactMatches);
+            return FindMostDerivedNewSlotMeth(exactMatches.AsSpan());
         }
 
         // Return any exact bindings that may exist. (This method is not defined on the
         //  Binder and is used by RuntimeType.)
-        public static PropertyInfo? ExactPropertyBinding(PropertyInfo[] match, Type? returnType, Type[]? types)
+        public static PropertyInfo? ExactPropertyBinding(ReadOnlySpan<PropertyInfo> match, Type? returnType, Type[]? types)
         {
-            ArgumentNullException.ThrowIfNull(match);
-
             PropertyInfo? bestMatch = null;
             int typesLength = (types != null) ? types.Length : 0;
             for (int i = 0; i < match.Length; i++)
@@ -1126,12 +1124,12 @@ private static int GetHierarchyDepth(Type t)
             return depth;
         }
 
-        internal static MethodBase? FindMostDerivedNewSlotMeth(MethodBase[] match, int cMatches)
+        internal static T? FindMostDerivedNewSlotMeth<T>(ReadOnlySpan<T> match) where T : MethodBase
         {
             int deepestHierarchy = 0;
-            MethodBase? methWithDeepestHierarchy = null;
+            T? methodWithDeepestHierarchy = null;
 
-            for (int i = 0; i < cMatches; i++)
+            for (int i = 0; i < match.Length; i++)
             {
                 // Calculate the depth of the hierarchy of the declaring type of the
                 // current method.
@@ -1141,18 +1139,18 @@ private static int GetHierarchyDepth(Type t)
                 // This can only happen if at least one is vararg or generic.
                 if (currentHierarchyDepth == deepestHierarchy)
                 {
-                    throw ThrowHelper.GetAmbiguousMatchException(methWithDeepestHierarchy!);
+                    throw ThrowHelper.GetAmbiguousMatchException(methodWithDeepestHierarchy!);
                 }
 
                 // Check to see if this method is on the most derived class.
                 if (currentHierarchyDepth > deepestHierarchy)
                 {
                     deepestHierarchy = currentHierarchyDepth;
-                    methWithDeepestHierarchy = match[i];
+                    methodWithDeepestHierarchy = match[i];
                 }
             }
 
-            return methWithDeepestHierarchy;
+            return methodWithDeepestHierarchy;
         }
 
         // This method will sort the vars array into the mapping order stored
diff --git a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/ListBuilder.cs b/src/libraries/System.Private.CoreLib/src/System/Reflection/ListBuilder.cs
similarity index 58%
rename from src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/ListBuilder.cs
rename to src/libraries/System.Private.CoreLib/src/System/Reflection/ListBuilder.cs
index 12ccb40f48aa27..5b8dd54ff92f06 100644
--- a/src/coreclr/nativeaot/System.Private.CoreLib/src/System/Reflection/Runtime/General/ListBuilder.cs
+++ b/src/libraries/System.Private.CoreLib/src/System/Reflection/ListBuilder.cs
@@ -2,23 +2,24 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 
-namespace System.Reflection.Runtime.General
+namespace System.Reflection
 {
-    //
-    // Struct-based list builder that's special cased to avoid allocations for lists of one element.
-    //
+    // Helper to build arrays. Special cased to avoid allocations for arrays of one element.
     internal struct ListBuilder<T> where T : class
     {
+        private T[]? _items;
+        private T _item;
+        private int _count;
+        private int _capacity;
+
         public ListBuilder(int capacity)
         {
             _items = null;
-            _item = null;
+            _item = null!;
             _count = 0;
             _capacity = capacity;
-#if DEBUG
-            _toArrayAlreadyCalled = false;
-#endif // DEBUG
         }
 
         public T this[int index]
@@ -32,23 +33,28 @@ public T this[int index]
 
         public T[] ToArray()
         {
-#if DEBUG
-            // ListBuilder does not always allocate a new array, though the ToArray() name connotates that it does (and in fact, we do pass the results
-            // of this method across api boundaries.) The minimizing of allocations is desirable, however, so instead, we restrict you to one call per ListBuilder.
-            Debug.Assert(!_toArrayAlreadyCalled, "Cannot call ListBuilder.ToArray() a second time. Copy the one you already got.");
-#endif // DEBUG
             if (_count == 0)
-                return Array.Empty<T>();
+                return [];
+
             if (_count == 1)
-                return new T[1] { _item };
+                return [_item];
 
-            Array.Resize(ref _items, _count);
+            if (_count == _items!.Length)
+                return _items;
 
-#if DEBUG
-            _toArrayAlreadyCalled = true;
-#endif // DEBUG
+            return _items.AsSpan(0, _count).ToArray();
+        }
+
+        [UnscopedRef]
+        public readonly ReadOnlySpan<T> AsSpan()
+        {
+            if (_count == 0)
+                return default;
+
+            if (_count == 1)
+                return new ReadOnlySpan<T>(in _item);
 
-            return _items;
+            return _items.AsSpan(0, _count);
         }
 
         public void CopyTo(object[] array, int index)
@@ -62,16 +68,10 @@ public void CopyTo(object[] array, int index)
                 return;
             }
 
-            Array.Copy(_items, 0, array, index, _count);
+            Array.Copy(_items!, 0, array, index, _count);
         }
 
-        public int Count
-        {
-            get
-            {
-                return _count;
-            }
-        }
+        public int Count => _count;
 
         public void Add(T item)
         {
@@ -85,6 +85,7 @@ public void Add(T item)
                 {
                     if (_capacity < 2)
                         _capacity = 4;
+
                     _items = new T[_capacity];
                     _items[0] = _item;
                 }
@@ -95,17 +96,10 @@ public void Add(T item)
                     _capacity = newCapacity;
                 }
 
-                _items[_count] = item;
+                _items![_count] = item;
             }
+
             _count++;
         }
-
-        private T[] _items;
-        private T _item;
-        private int _count;
-        private int _capacity;
-#if DEBUG
-        private bool _toArrayAlreadyCalled;
-#endif // DEBUG
     }
 }
diff --git a/src/mono/System.Private.CoreLib/src/System/RuntimeType.Mono.cs b/src/mono/System.Private.CoreLib/src/System/RuntimeType.Mono.cs
index c9e3d9ff4573a7..01577c29a88193 100644
--- a/src/mono/System.Private.CoreLib/src/System/RuntimeType.Mono.cs
+++ b/src/mono/System.Private.CoreLib/src/System/RuntimeType.Mono.cs
@@ -49,94 +49,6 @@ internal enum MemberListType
             HandleToInfo
         }
 
-        // Helper to build lists of MemberInfos. Special cased to avoid allocations for lists of one element.
-        private struct ListBuilder<T> where T : class?
-        {
-            private T[]? _items;
-            private T _item;
-            private int _count;
-            private int _capacity;
-
-            public ListBuilder(int capacity)
-            {
-                _items = null;
-                _item = null!;
-                _count = 0;
-                _capacity = capacity;
-            }
-
-            public T this[int index]
-            {
-                get
-                {
-                    Debug.Assert(index < Count);
-                    return (_items != null) ? _items[index] : _item;
-                }
-            }
-
-            public T[] ToArray()
-            {
-                if (_count == 0)
-                    return Array.Empty<T>();
-                if (_count == 1)
-                    return new T[1] { _item };
-
-                Array.Resize(ref _items, _count);
-                _capacity = _count;
-                return _items;
-            }
-
-            public void CopyTo(object?[] array, int index)
-            {
-                if (_count == 0)
-                    return;
-
-                if (_count == 1)
-                {
-                    array[index] = _item;
-                    return;
-                }
-
-                Array.Copy(_items!, 0, array, index, _count);
-            }
-
-            public int Count
-            {
-                get
-                {
-                    return _count;
-                }
-            }
-
-            public void Add(T item)
-            {
-                if (_count == 0)
-                {
-                    _item = item;
-                }
-                else
-                {
-                    if (_count == 1)
-                    {
-                        if (_capacity < 2)
-                            _capacity = 4;
-                        _items = new T[_capacity];
-                        _items[0] = _item;
-                    }
-                    else
-                    if (_capacity == _count)
-                    {
-                        int newCapacity = 2 * _capacity;
-                        Array.Resize(ref _items, newCapacity);
-                        _capacity = newCapacity;
-                    }
-
-                    _items![_count] = item;
-                }
-                _count++;
-            }
-        }
-
         #endregion
 
         #region Static Members
@@ -798,7 +710,7 @@ public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
                     }
 
                     // All the methods have the exact same name and sig so return the most derived one.
-                    return System.DefaultBinder.FindMostDerivedNewSlotMeth(candidates.ToArray(), candidates.Count) as MethodInfo;
+                    return System.DefaultBinder.FindMostDerivedNewSlotMeth(candidates.AsSpan());
                 }
             }
 
@@ -827,7 +739,7 @@ public override MemberInfo[] GetMembers(BindingFlags bindingAttr)
             }
 
             if ((bindingAttr & BindingFlags.ExactBinding) != 0)
-                return System.DefaultBinder.ExactBinding(candidates.ToArray(), types) as ConstructorInfo;
+                return System.DefaultBinder.ExactBinding(candidates.AsSpan(), types);
 
             binder ??= DefaultBinder;