diff --git a/src/vim9class.c b/src/vim9class.c
index 5249f40..560c5ae 100644
--- a/src/vim9class.c
+++ b/src/vim9class.c
@@ -4132,7 +4132,12 @@
 	return;
 
     if (object_tv->vval.v_object == NULL)
+    {
+	if (classinfo_tv->vval.v_class == NULL)
+	    // consider null_object as an instance of null_class
+	    rettv->vval.v_number = VVAL_TRUE;
 	return;
+    }
 
     for (; classinfo_tv->v_type != VAR_UNKNOWN; ++classinfo_tv)
     {