diff --git a/src/httpd.index.c b/src/httpd.index.c
index b776ac942..17f727c1f 100644
--- a/src/httpd.index.c
+++ b/src/httpd.index.c
@@ -177,7 +177,7 @@ static void _httpd_endpoint_app_index_file_read(tf_task_t* task, const char* pat
 		char* replacement = tf_strdup("<iframe srcdoc=\"");
 		size_t replacement_size = 0;
 		replacement = _append_encoded(replacement, state->data, state->size, &replacement_size);
-		_append_raw(replacement, &replacement_size, "\"", 1);
+		replacement = _append_raw(replacement, &replacement_size, "\"", 1);
 
 		size_t size = 0;
 		char* document = _replace(data, result, "<iframe", replacement, &size);