diff --git a/src/protocol/pool_proto_modules.c b/src/protocol/pool_proto_modules.c
index 4988325dc..e917db995 100644
--- a/src/protocol/pool_proto_modules.c
+++ b/src/protocol/pool_proto_modules.c
@@ -2960,6 +2960,14 @@ ProcessFrontendResponse(POOL_CONNECTION * frontend,
 					 * If data remains in the frontend write buffer, flush it
 					 * now.
 					 */
+					if (!pool_read_buffer_is_empty(frontend))
++					{
++						/* If data remains in the frontend buffer, flush it now. */
++						pool_flush(frontend);
++						elog(DEBUG5,
++							 "pending data flushed to frontend due to a flush message");
++					}
+
 					pool_flush(frontend);
 					elog(DEBUG5,
 						 "pending data flushed to frontend due to a flush message");
@@ -3398,6 +3406,12 @@ CopyDataRows(POOL_CONNECTION * frontend,
 					copy_count++;
 					continue;
 				}
+				/*
+				 * Flush (H) or Sync (S) messages should be ignored while in
+				 * the COPY IN mode.
+				 */
+				else if (kind == 'H' || kind == 'S')
+					continue;
 				else
 				{
 					if (pool_config->log_client_messages && copy_count != 0)