diff --git a/src/if_python3.c b/src/if_python3.c
index a62971e..57257e6 100644
--- a/src/if_python3.c
+++ b/src/if_python3.c
@@ -1817,6 +1817,10 @@
 	case VAR_DICT: ++rettv->vval.v_dict->dv_refcount; break;
 	case VAR_LIST: ++rettv->vval.v_list->lv_refcount; break;
 	case VAR_FUNC: func_ref(rettv->vval.v_string);    break;
+	case VAR_UNKNOWN:
+	    rettv->v_type = VAR_NUMBER;
+	    rettv->vval.v_number = 0;
+	    break;
     }
 }