diff --git a/src/protocol/pool_proto_modules.c b/src/protocol/pool_proto_modules.c
index a3b826032..6465fdb5a 100644
--- a/src/protocol/pool_proto_modules.c
+++ b/src/protocol/pool_proto_modules.c
@@ -3397,6 +3397,12 @@ 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)