diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5cb0ea96c..b5b11cd77 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -25,6 +25,7 @@ This document follows the conventions laid out in [Keep a CHANGELOG][].
 - Fixed runtime that fails loading when using pythonnet in an environment
   together with Nuitka
 - Fixes bug where delegates get casts (dotnetcore)
+- Determine size of interpreter longs at runtime
 
 ## [2.4.0][]
 
diff --git a/src/runtime/converter.cs b/src/runtime/converter.cs
index 5d8769a73..e7e047419 100644
--- a/src/runtime/converter.cs
+++ b/src/runtime/converter.cs
@@ -728,7 +728,20 @@ private static bool ToPrimitive(IntPtr value, Type obType, out object result, bo
                         }
                         goto type_error;
                     }
-                    uint ui = (uint)Runtime.PyLong_AsUnsignedLong(op);
+                    
+                    uint ui;
+                    try 
+                    {
+                        ui = Convert.ToUInt32(Runtime.PyLong_AsUnsignedLong(op));
+                    } catch (OverflowException)
+                    {
+                        // Probably wasn't an overflow in python but was in C# (e.g. if cpython
+                        // longs are 64 bit then 0xFFFFFFFF + 1 will not overflow in 
+                        // PyLong_AsUnsignedLong)
+                        Runtime.XDecref(op);
+                        goto overflow;
+                    }
+                    
 
                     if (Exceptions.ErrorOccurred())
                     {
diff --git a/src/runtime/runtime.cs b/src/runtime/runtime.cs
index 75f11492f..4985a57f5 100644
--- a/src/runtime/runtime.cs
+++ b/src/runtime/runtime.cs
@@ -1036,8 +1036,21 @@ internal static bool PyLong_Check(IntPtr ob)
         [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
         internal static extern IntPtr PyLong_FromLong(long value);
 
-        [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern IntPtr PyLong_FromUnsignedLong(uint value);
+        [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl,
+            EntryPoint = "PyLong_FromUnsignedLong")]
+        internal static extern IntPtr PyLong_FromUnsignedLong32(uint value);
+
+        [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl,
+            EntryPoint = "PyLong_FromUnsignedLong")]
+        internal static extern IntPtr PyLong_FromUnsignedLong64(ulong value);
+
+        internal static IntPtr PyLong_FromUnsignedLong(object value)
+        {
+            if(Is32Bit || IsWindows)
+                return PyLong_FromUnsignedLong32(Convert.ToUInt32(value));
+            else
+                return PyLong_FromUnsignedLong64(Convert.ToUInt64(value));
+        }
 
         [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
         internal static extern IntPtr PyLong_FromDouble(double value);
@@ -1054,8 +1067,21 @@ internal static bool PyLong_Check(IntPtr ob)
         [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
         internal static extern int PyLong_AsLong(IntPtr value);
 
-        [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
-        internal static extern uint PyLong_AsUnsignedLong(IntPtr value);
+        [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl,
+            EntryPoint = "PyLong_AsUnsignedLong")]
+        internal static extern uint PyLong_AsUnsignedLong32(IntPtr value);
+
+        [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl,
+            EntryPoint = "PyLong_AsUnsignedLong")]
+        internal static extern ulong PyLong_AsUnsignedLong64(IntPtr value);
+
+        internal static object PyLong_AsUnsignedLong(IntPtr value)
+        {
+            if (Is32Bit || IsWindows)
+                return PyLong_AsUnsignedLong32(value);
+            else
+                return PyLong_AsUnsignedLong64(value);
+        }
 
         [DllImport(_PythonDll, CallingConvention = CallingConvention.Cdecl)]
         internal static extern long PyLong_AsLongLong(IntPtr value);