diff --git a/docker_challenges/__init__.py b/docker_challenges/__init__.py
index 190ef35..0aaa8da 100644
--- a/docker_challenges/__init__.py
+++ b/docker_challenges/__init__.py
@@ -276,7 +276,8 @@ def get_unavailable_ports(docker):
     for i in r.json():
         if not i['Ports'] == []:
             for p in i['Ports']:
-                result.append(p['PublicPort'])
+                if 'PublicPort'in p:
+                    result.append(p['PublicPort'])
     return result