diff --git a/runtime/onert/core/include/ir/train/operation/UntrainableOperation.h b/runtime/onert/core/include/ir/train/operation/UntrainableOperation.h
index a291dc091cc..3f27effc29e 100644
--- a/runtime/onert/core/include/ir/train/operation/UntrainableOperation.h
+++ b/runtime/onert/core/include/ir/train/operation/UntrainableOperation.h
@@ -51,7 +51,7 @@ class UntrainableOperation : public OperationType, public TrainableOperation
   void accept(OperationVisitor &v) const override { v.visit(*this); }
   void accept(TrainableOperationVisitor &) const override
   {
-    throw std::runtime_error(OperationType::name() + "operation is not trainable yet");
+    throw std::runtime_error(OperationType::name() + " operation is not trainable yet");
   }
   bool hasTrainableParameter() const override { return false; }
 };