diff --git a/src/sync.c b/src/sync.c
index 3600da70..5519c757 100644
--- a/src/sync.c
+++ b/src/sync.c
@@ -70,6 +70,7 @@ getdns_general_sync(struct getdns_context *context,
 {
 	getdns_return_t response_status;
     RETURN_IF_NULL(context, GETDNS_RETURN_BAD_CONTEXT);
+    RETURN_IF_NULL(response, GETDNS_RETURN_INVALID_PARAMETER);
 	response_status = validate_extensions(extensions);
 	if (response_status == GETDNS_RETURN_GOOD) {
 		response_status = getdns_general_ub(context->unbound_sync,