diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index d571fd897a4..f2039d4ed66 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -3273,6 +3273,7 @@ class BitcodeErrorCategoryType : public _do_message {
     case BitcodeReader::InvalidValue:
       return "Invalid value";
     }
+    llvm_unreachable("Unknown error type!");
   }
 };
 }