diff --git a/degesch.c b/degesch.c
index 5621f96..e42f015 100644
--- a/degesch.c
+++ b/degesch.c
@@ -7649,7 +7649,11 @@ lua_plugin_handle_string_filter_result (struct lua_plugin *self,
 {
 	lua_State *L = self->L;
 	if (lua_isnil (L, -1))
+	{
+		free (*original);
+		*original = NULL;
 		return true;
+	}
 	if (!lua_isstring (L, -1))
 		FAIL ("must return either a string or nil");