diff --git a/src/testdir/test_vim9_assign.vim b/src/testdir/test_vim9_assign.vim
index 2a21ca0..2d137a3 100644
--- a/src/testdir/test_vim9_assign.vim
+++ b/src/testdir/test_vim9_assign.vim
@@ -1091,6 +1091,13 @@
       assert_equal(123, FuncRef_Any())
   END
   CheckScriptSuccess(lines)
+
+  lines =<< trim END
+      var Ref: func(number)
+      Ref = (j) => !j
+  END
+  CheckDefFailure(lines, 'E1012: Type mismatch; expected func(number) but got func(any): bool')
+  CheckScriptFailure(['vim9script'] + lines, 'E1012: Type mismatch; expected func(number) but got func(any): any')
 enddef
 
 def Test_heredoc()
diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index c26f2af..9f19ebd 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -1508,7 +1508,7 @@
       'delfunc g:NotExist'], 'E700:')
 enddef
 
-def RefFunc(Ref: func(string): string): string
+def RefFunc(Ref: func(any): any): string
   return Ref('more')
 enddef