diff --git a/include/llvm/IR/DataLayout.h b/include/llvm/IR/DataLayout.h
index 520d4ede181..9ffa056355d 100644
--- a/include/llvm/IR/DataLayout.h
+++ b/include/llvm/IR/DataLayout.h
@@ -257,6 +257,7 @@ public:
     case MM_COFF:
       return '_';
     }
+    llvm_unreachable("invalid mangling mode");
   }
 
   const char *getPrivateGlobalPrefix() const {
@@ -271,6 +272,7 @@ public:
     case MM_COFF:
       return "L";
     }
+    llvm_unreachable("invalid mangling mode");
   }
 
   static const char *getManglingComponent(const Triple &T);