diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -210,7 +210,8 @@
   This fixes `GH51182 <https://github.com/llvm/llvm-project/issues/51182>`
 - Fixes an assert crash caused by looking up missing vtable information on ``consteval``
   virtual functions. Fixes `GH55065 <https://github.com/llvm/llvm-project/issues/55065>`_.
-
+- Fixed a crash during template instantiation on a conversion operator during constraint
+  evaulation. Fixes `GH50891 <https://github.com/llvm/llvm-project/issues/50891>`_.
 
 C++2b Feature Support
 ^^^^^^^^^^^^^^^^^^^^^
diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -4009,6 +4009,16 @@
     }
   }
 
+  if (!S.CodeSynthesisContexts.empty())
+    llvm::errs() << "Kind: " << S.CodeSynthesisContexts.back().Kind << "\n";
+
+  // Avoid an infinite template expansion loop in requirements checking by
+  // skipping the conversion functions check.
+  bool InRequirementInstantiation =
+      !S.CodeSynthesisContexts.empty() &&
+      S.CodeSynthesisContexts.back().Kind ==
+          Sema::CodeSynthesisContext::RequirementInstantiation;
+
   // FIXME: Work around a bug in C++17 guaranteed copy elision.
   //
   // When initializing an object of class type T by constructor
@@ -4021,7 +4031,7 @@
   // Note: SecondStepOfCopyInit is only ever true in this case when
   // evaluating whether to produce a C++98 compatibility warning.
   if (S.getLangOpts().CPlusPlus17 && Args.size() == 1 &&
-      !SecondStepOfCopyInit) {
+      !SecondStepOfCopyInit && !InRequirementInstantiation) {
     Expr *Initializer = Args[0];
     auto *SourceRD = Initializer->getType()->getAsCXXRecordDecl();
     if (SourceRD && S.isCompleteType(DeclLoc, Initializer->getType())) {
diff --git a/clang/test/SemaTemplate/concepts.cpp b/clang/test/SemaTemplate/concepts.cpp
--- a/clang/test/SemaTemplate/concepts.cpp
+++ b/clang/test/SemaTemplate/concepts.cpp
@@ -256,3 +256,20 @@
 C auto **&j2 = g();  // expected-error {{deduced type 'int' does not satisfy 'C'}}
 C auto **&&j3 = g(); // expected-error {{deduced type 'int' does not satisfy 'C'}}
 }
+
+namespace Issue50891 {
+
+template <typename T>
+concept Numeric =
+    requires(T a) {
+        foo(a);
+    };
+
+struct Deferred {
+    friend void foo(Deferred);
+    template <Numeric TO> operator TO();
+};
+
+static_assert(Numeric<Deferred>); // should not crash clang
+
+} // namespace Issue50891