diff --git a/dbms/include/DB/DataStreams/UnionBlockInputStream.h b/dbms/include/DB/DataStreams/UnionBlockInputStream.h
index 9ed197970da..6d250384f4c 100644
--- a/dbms/include/DB/DataStreams/UnionBlockInputStream.h
+++ b/dbms/include/DB/DataStreams/UnionBlockInputStream.h
@@ -37,8 +37,8 @@ class UnionBlockInputStream : public IProfilingBlockInputStream
 public:
 	UnionBlockInputStream(BlockInputStreams inputs_, unsigned max_threads_ = 1)
 		: max_threads(std::min(inputs_.size(), static_cast<size_t>(max_threads_))),
-		output_queue(max_threads), exhausted_inputs(0), finish(false), all_read(false),
-		log(&Logger::get("UnionBlockInputStream"))
+		output_queue(max_threads), exhausted_inputs(0), finish(false),
+		pushed_end_of_output_queue(false), all_read(false), log(&Logger::get("UnionBlockInputStream"))
 	{
 		children.insert(children.end(), inputs_.begin(), inputs_.end());
 
@@ -276,7 +276,11 @@ private:
 				Poco::ScopedLock<Poco::FastMutex> lock(parent.mutex);
 
 				/// Отдаём в основной поток пустой блок, что означает, что данных больше нет.
-				parent.output_queue.push(OutputData());
+				if (!parent.pushed_end_of_output_queue)
+				{
+					parent.pushed_end_of_output_queue = true;
+					parent.output_queue.push(OutputData());
+				}
 			}
 		}
 
@@ -318,6 +322,8 @@ private:
 
 	/// Завершить работу потоков (раньше, чем иссякнут источники).
 	volatile bool finish;
+	/// Положили ли в output_queue пустой блок.
+	bool pushed_end_of_output_queue;
 	bool all_read;
 
 	Logger * log;