diff --git a/src/testdir/test_vim9_class.vim b/src/testdir/test_vim9_class.vim
index fa621b2..1021114 100644
--- a/src/testdir/test_vim9_class.vim
+++ b/src/testdir/test_vim9_class.vim
@@ -3032,6 +3032,10 @@
       assert_true(instanceof(a3, [Base1, Base2, Intf1]))
     enddef
     Foo()
+
+    var o_null: Base1
+    assert_false(instanceof(o_null, Base1))
+
   END
   v9.CheckSourceSuccess(lines)
 enddef
diff --git a/src/version.c b/src/version.c
index c2bef2f..79b1e11 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1911,
+/**/
     1910,
 /**/
     1909,
diff --git a/src/vim9class.c b/src/vim9class.c
index da862f2..f122f90 100644
--- a/src/vim9class.c
+++ b/src/vim9class.c
@@ -2865,6 +2865,9 @@
 	    || check_for_class_or_list_arg(argvars, 1) == FAIL)
 	return;
 
+    if (object_tv->vval.v_object == NULL)
+	return;
+
     if (classinfo_tv->v_type == VAR_LIST)
     {
 	FOR_ALL_LIST_ITEMS(classinfo_tv->vval.v_list, li)