diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index b13ddab..db0b093 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -3115,7 +3115,7 @@ PQsendFlushRequest(PGconn *conn)
 	{
 		appendPQExpBufferStr(&conn->errorMessage,
 							 libpq_gettext("another command is already in progress\n"));
-		return false;
+		return 0;
 	}
 
 	if (pqPutMsgStart('H', conn) < 0 ||