diff --git a/src/errors.h b/src/errors.h
index f1c36ad..445a9b8 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -3452,4 +3452,6 @@
 #ifdef FEAT_EVAL
 EXTERN char e_cannot_use_non_null_object[]
 	INIT(= N_("E1362: Cannot use a non-null object"));
+EXTERN char e_incomplete_type[]
+	INIT(= N_("E1363: Incomplete type"));
 #endif
diff --git a/src/testdir/test_vim9_class.vim b/src/testdir/test_vim9_class.vim
index c228f26..bc8a8e1 100644
--- a/src/testdir/test_vim9_class.vim
+++ b/src/testdir/test_vim9_class.vim
@@ -272,6 +272,25 @@
       echo Colorscheme.new(bg).GetBackground()
   END
   v9.CheckScriptFailure(lines, 'E1012: Type mismatch; expected object<Background> but got object<Unknown>')
+
+  # TODO: this should not give an error but be handled at runtime
+  lines =<< trim END
+      vim9script
+
+      class Class
+          this.id: string
+          def Method1()
+              echo 'Method1' .. this.id
+          enddef
+      endclass
+
+      var obj = null_object
+      def Func()
+          obj.Method1()
+      enddef
+      Func()
+  END
+  v9.CheckScriptFailure(lines, 'E1363:')
 enddef
 
 def Test_class_member_initializer()
diff --git a/src/version.c b/src/version.c
index 1caf5b2..8f26bdf 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1375,
+/**/
     1374,
 /**/
     1373,
diff --git a/src/vim9expr.c b/src/vim9expr.c
index b8458aa..d600cb0 100644
--- a/src/vim9expr.c
+++ b/src/vim9expr.c
@@ -293,6 +293,13 @@
 	}
     }
 
+    if (cl == NULL)
+    {
+	// TODO: this should not give an error but be handled at runtime
+	emsg(_(e_incomplete_type));
+	return FAIL;
+    }
+
     ++*arg;
     char_u *name = *arg;
     char_u *name_end = find_name_end(name, NULL, NULL, FNE_CHECK_START);