diff --git a/slirp/misc.c b/slirp/misc.c
index a0f104be5e..eae9596a55 100644
--- a/slirp/misc.c
+++ b/slirp/misc.c
@@ -37,13 +37,6 @@ int add_exec(struct gfwd_list **ex_ptr, void *chardev, const char *cmdline,
 {
 	struct gfwd_list *tmp_ptr;
 
-	/* First, check if the port is "bound" */
-	for (tmp_ptr = *ex_ptr; tmp_ptr; tmp_ptr = tmp_ptr->ex_next) {
-		if (port == tmp_ptr->ex_fport &&
-		    addr.s_addr == tmp_ptr->ex_addr.s_addr)
-			return -1;
-	}
-
 	tmp_ptr = *ex_ptr;
 	*ex_ptr = g_new0(struct gfwd_list, 1);
 	(*ex_ptr)->ex_fport = port;
diff --git a/slirp/slirp.c b/slirp/slirp.c
index 851462a4cd..882d28a4de 100644
--- a/slirp/slirp.c
+++ b/slirp/slirp.c
@@ -1046,9 +1046,11 @@ int slirp_add_hostfwd(Slirp *slirp, int is_udp, struct in_addr host_addr,
     return 0;
 }
 
-int slirp_add_exec(Slirp *slirp, void *chardev, const char *cmdline,
-                   struct in_addr *guest_addr, int guest_port)
+static bool
+check_guestfwd(Slirp *slirp, struct in_addr *guest_addr, int guest_port)
 {
+    struct gfwd_list *tmp_ptr;
+
     if (!guest_addr->s_addr) {
         guest_addr->s_addr = slirp->vnetwork_addr.s_addr |
             (htonl(0x0204) & ~slirp->vnetwork_mask.s_addr);
@@ -1057,6 +1059,23 @@ int slirp_add_exec(Slirp *slirp, void *chardev, const char *cmdline,
         slirp->vnetwork_addr.s_addr ||
         guest_addr->s_addr == slirp->vhost_addr.s_addr ||
         guest_addr->s_addr == slirp->vnameserver_addr.s_addr) {
+        return false;
+    }
+
+    /* check if the port is "bound" */
+    for (tmp_ptr = slirp->guestfwd_list; tmp_ptr; tmp_ptr = tmp_ptr->ex_next) {
+        if (guest_port == tmp_ptr->ex_fport &&
+            guest_addr->s_addr == tmp_ptr->ex_addr.s_addr)
+            return false;
+    }
+
+    return true;
+}
+
+int slirp_add_exec(Slirp *slirp, void *chardev, const char *cmdline,
+                   struct in_addr *guest_addr, int guest_port)
+{
+    if (!check_guestfwd(slirp, guest_addr, guest_port)) {
         return -1;
     }