diff --git a/src/Processors/Transforms/Streaming/WatermarkTransformWithSubstream.cpp b/src/Processors/Transforms/Streaming/WatermarkTransformWithSubstream.cpp
index 151827486e..46a66a9fd3 100644
--- a/src/Processors/Transforms/Streaming/WatermarkTransformWithSubstream.cpp
+++ b/src/Processors/Transforms/Streaming/WatermarkTransformWithSubstream.cpp
@@ -107,6 +107,8 @@ void WatermarkTransformWithSubstream::work()
     assert(output_iter == output_chunks.end());
     output_chunks.clear();
 
+    SCOPE_EXIT({ output_iter = output_chunks.begin(); });
+
     /// We will need clear input_chunk for next run
     Chunk process_chunk;
     process_chunk.swap(input_chunk);