diff --git a/clang/lib/AST/ExprConstantMeta.cpp b/clang/lib/AST/ExprConstantMeta.cpp
index 0808f3124833..bc23ad41dbe5 100644
--- a/clang/lib/AST/ExprConstantMeta.cpp
+++ b/clang/lib/AST/ExprConstantMeta.cpp
@@ -1664,6 +1664,7 @@ StringRef DescriptionOf(APValue RV, bool Granular = true) {
     return "an annotation";
   }
   }
+  llvm_unreachable("unknown reflection");
 }
 
 bool DiagnoseReflectionKind(DiagFn Diagnoser, SourceRange Range,