diff --git a/mlir/lib/Target/Cpp/TranslateToCpp.cpp b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
index aae254a14459..859c6f015109 100644
--- a/mlir/lib/Target/Cpp/TranslateToCpp.cpp
+++ b/mlir/lib/Target/Cpp/TranslateToCpp.cpp
@@ -668,6 +668,7 @@ bool CppEmitter::shouldMapToUnsigned(IntegerType::SignednessSemantics val) {
   case IntegerType::Unsigned:
     return true;
   }
+  llvm_unreachable("Unexpected IntegerType::SignednessSemantics");
 }
 
 bool CppEmitter::hasValueInScope(Value val) { return valueMapper.count(val); }