diff --git a/net/filter.c b/net/filter.c
index c7cc6615dc..389f3b0bfe 100644
--- a/net/filter.c
+++ b/net/filter.c
@@ -130,6 +130,7 @@ static void netfilter_set_netdev_id(Object *obj, const char *str, Error **errp)
 {
     NetFilterState *nf = NETFILTER(obj);
 
+    g_free(nf->netdev_id);
     nf->netdev_id = g_strdup(str);
 }
 
@@ -182,6 +183,7 @@ static void netfilter_set_position(Object *obj, const char *str, Error **errp)
 {
     NetFilterState *nf = NETFILTER(obj);
 
+    g_free(nf->position);
     nf->position = g_strdup(str);
 }