diff --git a/parser.c b/parser.c
index 3a7d0d0..e12ff98 100644
--- a/parser.c
+++ b/parser.c
@@ -219,7 +219,7 @@ bool parser_do(parser_t *parser)
             }
 
             if (func)
-                func->builtin = parser_token(parser)->constval.i;
+                func->builtin = -parser_token(parser)->constval.i;
         } else if (parser->tok == '{') {
             /* function body */
         } else {