diff --git a/src/document/html/parser/forms.c b/src/document/html/parser/forms.c
index 8ec5a5371..0bbaf1345 100644
--- a/src/document/html/parser/forms.c
+++ b/src/document/html/parser/forms.c
@@ -78,7 +78,7 @@ html_form(struct html_context *html_context, unsigned char *a)
* Mozilla handles action="" as action="" which seems
* reasonable. (bug 615) */
if (al && *al) {
- form->action = join_urls(html_context->base_href, trim_chars(al, ' ', 0));
+ form->action = join_urls(html_context->base_href, trim_chars(al, ' ', NULL));
mem_free(al);
} else {