diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -211,16 +211,16 @@
 - Correctly set expression evaluation context as 'immediate function context' in
   consteval functions.
   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>`_.
-
 - Skip rebuilding lambda expressions in arguments of immediate invocations.
   This fixes `GH56183 <https://github.com/llvm/llvm-project/issues/56183>`_,
   `GH51695 <https://github.com/llvm/llvm-project/issues/51695>`_,
   `GH50455 <https://github.com/llvm/llvm-project/issues/50455>`_,
   `GH54872 <https://github.com/llvm/llvm-project/issues/54872>`_,
   `GH54587 <https://github.com/llvm/llvm-project/issues/54587>`_.
+- 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
@@ -4020,8 +4020,14 @@
   //
   // Note: SecondStepOfCopyInit is only ever true in this case when
   // evaluating whether to produce a C++98 compatibility warning.
+  //
+  // The last check avoids an infinite template expansion loop in
+  // requirements checking by skipping the conversion functions check.
   if (S.getLangOpts().CPlusPlus17 && Args.size() == 1 &&
-      !SecondStepOfCopyInit) {
+      !SecondStepOfCopyInit &&
+      (S.CodeSynthesisContexts.empty() ||
+       S.CodeSynthesisContexts.back().Kind !=
+           Sema::CodeSynthesisContext::RequirementInstantiation)) {
     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