diff --git a/mlir/lib/Dialect/Vector/VectorTransforms.cpp b/mlir/lib/Dialect/Vector/VectorTransforms.cpp
index f7a2c3e5b51c..3d8353d0a9ad 100644
--- a/mlir/lib/Dialect/Vector/VectorTransforms.cpp
+++ b/mlir/lib/Dialect/Vector/VectorTransforms.cpp
@@ -3749,6 +3749,8 @@ struct TwoDimMultiReductionToReduction
         return "or";
       case vector::CombiningKind::XOR:
         return "xor";
+      default:
+        llvm_unreachable("unknwon combining kind");
       }
     };