diff --git a/src/Server/TCPHandler.cpp b/src/Server/TCPHandler.cpp
index 14a2bceebf1..b59fe2c1849 100644
--- a/src/Server/TCPHandler.cpp
+++ b/src/Server/TCPHandler.cpp
@@ -387,7 +387,7 @@ void TCPHandler::runImpl()
 
             query_scope.emplace(query_context, /* fatal_error_callback */ [this]
             {
-                std::lock_guard lock(fatal_error_mutex);
+                std::lock_guard lock(out_mutex);
                 sendLogs();
             });
 
@@ -475,7 +475,7 @@ void TCPHandler::runImpl()
                 Stopwatch watch;
                 CurrentMetrics::Increment callback_metric_increment(CurrentMetrics::ReadTaskRequestsSent);
 
-                std::lock_guard lock(task_callback_mutex);
+                std::scoped_lock lock(out_mutex, task_callback_mutex);
 
                 if (state.cancellation_status == CancellationStatus::FULLY_CANCELLED)
                     return {};
@@ -491,7 +491,7 @@ void TCPHandler::runImpl()
             {
                 Stopwatch watch;
                 CurrentMetrics::Increment callback_metric_increment(CurrentMetrics::MergeTreeAllRangesAnnouncementsSent);
-                std::lock_guard lock(task_callback_mutex);
+                std::scoped_lock lock(out_mutex, task_callback_mutex);
 
                 if (state.cancellation_status == CancellationStatus::FULLY_CANCELLED)
                     return;
@@ -505,7 +505,7 @@ void TCPHandler::runImpl()
             {
                 Stopwatch watch;
                 CurrentMetrics::Increment callback_metric_increment(CurrentMetrics::MergeTreeReadTaskRequestsSent);
-                std::lock_guard lock(task_callback_mutex);
+                std::scoped_lock lock(out_mutex, task_callback_mutex);
 
                 if (state.cancellation_status == CancellationStatus::FULLY_CANCELLED)
                     return std::nullopt;
@@ -553,7 +553,7 @@ void TCPHandler::runImpl()
                     {
                         auto callback = [this]()
                         {
-                            std::scoped_lock lock(task_callback_mutex, fatal_error_mutex);
+                            std::scoped_lock lock(out_mutex, task_callback_mutex);
 
                             if (getQueryCancellationStatus() == CancellationStatus::FULLY_CANCELLED)
                                 return true;
@@ -572,7 +572,7 @@ void TCPHandler::runImpl()
 
                 finish_or_cancel();
 
-                std::lock_guard lock(task_callback_mutex);
+                std::lock_guard lock(out_mutex);
 
                 /// Send final progress after calling onFinish(), since it will update the progress.
                 ///
@@ -595,7 +595,7 @@ void TCPHandler::runImpl()
                 break;
 
             {
-                std::lock_guard lock(task_callback_mutex);
+                std::lock_guard lock(out_mutex);
                 sendLogs();
                 sendEndOfStream();
             }
@@ -1014,7 +1014,7 @@ void TCPHandler::processOrdinaryQuery()
 
     if (query_context->getSettingsRef().allow_experimental_query_deduplication)
     {
-        std::lock_guard lock(task_callback_mutex);
+        std::lock_guard lock(out_mutex);
         sendPartUUIDs();
     }
 
@@ -1024,13 +1024,13 @@ void TCPHandler::processOrdinaryQuery()
 
         if (header)
         {
-            std::lock_guard lock(task_callback_mutex);
+            std::lock_guard lock(out_mutex);
             sendData(header);
         }
     }
 
     /// Defer locking to cover a part of the scope below and everything after it
-    std::unique_lock progress_lock(task_callback_mutex, std::defer_lock);
+    std::unique_lock out_lock(out_mutex, std::defer_lock);
 
     {
         PullingAsyncPipelineExecutor executor(pipeline);
@@ -1056,6 +1056,9 @@ void TCPHandler::processOrdinaryQuery()
                 executor.cancelReading();
             }
 
+            lock.unlock();
+            out_lock.lock();
+
             if (after_send_progress.elapsed() / 1000 >= interactive_delay)
             {
                 /// Some time passed and there is a progress.
@@ -1071,12 +1074,14 @@ void TCPHandler::processOrdinaryQuery()
                 if (!state.io.null_format)
                     sendData(block);
             }
+
+            out_lock.unlock();
         }
 
         /// This lock wasn't acquired before and we make .lock() call here
         /// so everything under this line is covered even together
         /// with sendProgress() out of the scope
-        progress_lock.lock();
+        out_lock.lock();
 
         /** If data has run out, we will send the profiling data and total values to
           * the last zero block to be able to use
diff --git a/src/Server/TCPHandler.h b/src/Server/TCPHandler.h
index 75e36836b63..7569a1272a6 100644
--- a/src/Server/TCPHandler.h
+++ b/src/Server/TCPHandler.h
@@ -225,8 +225,13 @@ private:
     std::optional<UInt64> nonce;
     String cluster;
 
+    /// `out_mutex` protects `out` (WriteBuffer).
+    /// So it is used for method sendData(), sendProgress(), sendLogs(), etc.
+    std::mutex out_mutex;
+    /// `task_callback_mutex` protects tasks callbacks.
+    /// Inside these callbacks we might also change cancellation status,
+    /// so it also protects cancellation status checks.
     std::mutex task_callback_mutex;
-    std::mutex fatal_error_mutex;
 
     /// At the moment, only one ongoing query in the connection is supported at a time.
     QueryState state;