diff --git a/src/hlua.c b/src/hlua.c
index 6c7a87913..1b86e9199 100644
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -12000,7 +12000,7 @@ static int hlua_filter_callback(struct stream *s, struct filter *filter, const c
 		goto end;
 
 	if (!HLUA_IS_RUNNING(flt_hlua)) {
-		int extra_idx = lua_gettop(flt_hlua->T);
+		int extra_idx;
 
 		/* The following Lua calls can fail. */
 		if (!SET_SAFE_LJMP(flt_hlua)) {
@@ -12014,6 +12014,8 @@ static int hlua_filter_callback(struct stream *s, struct filter *filter, const c
 			goto end;
 		}
 
+		extra_idx = lua_gettop(flt_hlua->T);
+
 		/* Check stack size. */
 		if (!lua_checkstack(flt_hlua->T, 3)) {
 			SEND_ERR(s->be, "Lua filter '%s': full stack.\n", conf->reg->name);