diff --git a/clang/lib/Analysis/FlowSensitive/Value.cpp b/clang/lib/Analysis/FlowSensitive/Value.cpp
index 80dde7c8d5823..349f873f1e6c4 100644
--- a/clang/lib/Analysis/FlowSensitive/Value.cpp
+++ b/clang/lib/Analysis/FlowSensitive/Value.cpp
@@ -47,6 +47,7 @@ raw_ostream &operator<<(raw_ostream &OS, const Value &Val) {
   case Value::Kind::FormulaBool:
     return OS << "FormulaBool(" << cast<FormulaBoolValue>(Val).formula() << ")";
   }
+  llvm_unreachable("Unknown clang::dataflow::Value::Kind enum");
 }
 
 } // namespace dataflow