diff --git a/src/Processors/Executors/PullingPipelineExecutor.h b/src/Processors/Executors/PullingPipelineExecutor.h
index e51d007e7b1..f3b06fc618a 100644
--- a/src/Processors/Executors/PullingPipelineExecutor.h
+++ b/src/Processors/Executors/PullingPipelineExecutor.h
@@ -42,6 +42,7 @@ public:
     /// Get query profile info.
     BlockStreamProfileInfo & getProfileInfo();
 
+    /// Internal executor data.
     struct Data;
 
 private: