diff --git a/src/util.h b/src/util.h
index cf197084..49833dee 100755
--- a/src/util.h
+++ b/src/util.h
@@ -886,6 +886,7 @@ public:
         case OT_ANDROID: return "Android"; break;
         case OT_I_OS:    return "iOS";     break;
         case OT_UNIX:    return "Unix";    break;
+        default:         return "Unknown"; break;
         }
     }