diff --git a/clang/include/clang/Basic/HeaderInclude.h b/clang/include/clang/Basic/HeaderInclude.h
index 7a1a08ba617af..83c26543bbd3b 100644
--- a/clang/include/clang/Basic/HeaderInclude.h
+++ b/clang/include/clang/Basic/HeaderInclude.h
@@ -54,6 +54,7 @@ inline const char *headerIncludeFormatKindToString(HeaderIncludeFormatKind K) {
   case HIFMT_JSON:
     return "json";
   }
+  llvm_unreachable("Unknown HeaderIncludeFormatKind enum");
 }
 
 inline const char *
@@ -64,6 +65,7 @@ headerIncludeFilteringKindToString(HeaderIncludeFilteringKind K) {
   case HIFIL_Only_Direct_System:
     return "only-direct-system";
   }
+  llvm_unreachable("Unknown HeaderIncludeFilteringKind enum");
 }
 
 } // end namespace clang