diff --git a/src/frontend/parse.c b/src/frontend/parse.c
index 2dba28d34..2c6e9d0ff 100644
--- a/src/frontend/parse.c
+++ b/src/frontend/parse.c
@@ -307,6 +307,7 @@ struct pnode *PP_mkfnode(const char *func, struct pnode *arg)
         /* Give the user-defined functions a try. */
         q = ft_substdef(func, arg);
         if (q) { /* found */
+            free_pnode(arg);
             return q;
         }
     }