diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index f5cd1fbeabcfe..8a463f9aca0c9 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -529,6 +529,8 @@ Bug Fixes to C++ Support
 - Clang now issues an error when placement new is used to modify a const-qualified variable
   in a ``constexpr`` function. (#GH131432)
 - Clang now emits a warning when class template argument deduction for alias templates is used in C++17. (#GH133806)
+- Fix a crash when checking the template template parameters of a dependent lambda appearing in an alias declaration.
+  (#GH136432), (#GH137014), (#GH138018)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index 4d07efd58f518..9095575ee1175 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -1696,7 +1696,11 @@ static NamedDecl* getLambdaCallOperatorHelper(const CXXRecordDecl &RD) {
       RD.getASTContext().DeclarationNames.getCXXOperatorName(OO_Call);
 
   DeclContext::lookup_result Calls = RD.lookup(Name);
-  assert(!Calls.empty() && "Missing lambda call operator!");
+
+  // This can happen while building the lambda.
+  if (Calls.empty())
+    return nullptr;
+
   assert(allLookupResultsAreTheSame(Calls) &&
          "More than one lambda call operator!");
 
diff --git a/clang/test/SemaCXX/lambda-unevaluated.cpp b/clang/test/SemaCXX/lambda-unevaluated.cpp
index a9bcab58464e2..40f8a729fd912 100644
--- a/clang/test/SemaCXX/lambda-unevaluated.cpp
+++ b/clang/test/SemaCXX/lambda-unevaluated.cpp
@@ -266,3 +266,19 @@ void func() {
 }
 
 } // namespace GH88081
+
+namespace GH138018 {
+
+template <typename T> struct vec {};
+
+auto structure_to_typelist(auto)  {
+    return []<template <typename> typename T>(T<int>) {
+        return 0;
+    }(vec<int>{});
+}
+
+template <typename T> using helper = decltype(structure_to_typelist(T{}));
+static_assert(__is_same_as(int, helper<int>));
+
+
+} // namespace GH138018