diff --git a/server.c b/server.c
index f6ac3a9..a007c0b 100644
--- a/server.c
+++ b/server.c
@@ -133,7 +133,7 @@ int jb_server_client_assign_unique_name(struct jb_server *s, int i)
 int jb_server_client_assign_own_name(struct jb_server *s, int i, char *name)
 {
     struct jb_client *c = &s->clients[i];
-    if (c->owned_name_index != -1) {
+    if (c->owned_name_index != -1 || !name || *name == ':' || *name == '\0') {
         return -1;
     }