diff --git a/include/clang/Parse/Parser.h b/include/clang/Parse/Parser.h
index e1609c39997c13c44293e04c3cf3e791ac846225..611c69e93342eca290f49b88577b1e807af3cfd5 100644
--- a/include/clang/Parse/Parser.h
+++ b/include/clang/Parse/Parser.h
@@ -1654,6 +1654,8 @@ private:
   /// trailing-type-specifier)?
   static bool isTypeSpecifier(DeclSpecContext DSC) {
     switch (DSC) {
+    default:
+      llvm_unreachable("Missing DeclSpecContext case");
     case DSC_normal:
     case DSC_class:
     case DSC_top_level: