diff --git a/src/testdir/test_vim9_func.vim b/src/testdir/test_vim9_func.vim
index cdaba5a..cea25a4 100644
--- a/src/testdir/test_vim9_func.vim
+++ b/src/testdir/test_vim9_func.vim
@@ -1669,6 +1669,18 @@
 
   unlet g:UseArg
   unlet g:UseVararg
+
+  var lines =<< trim END
+      vim9script
+      def Test(Fun: func(number): number): list<number>
+        return map([1, 2, 3], (_, i) => Fun(i))
+      enddef
+      def Inc(nr: number): number
+        return nr + 2
+      enddef
+      assert_equal([3, 4, 5], Test(Inc))
+  END
+  CheckScriptSuccess(lines)
 enddef
 
 def MakeGetAndAppendRefs()
diff --git a/src/version.c b/src/version.c
index 60f8a71..465b5b0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2504,
+/**/
     2503,
 /**/
     2502,
diff --git a/src/vim9compile.c b/src/vim9compile.c
index 4dfb42f..b4b9c28 100644
--- a/src/vim9compile.c
+++ b/src/vim9compile.c
@@ -261,7 +261,8 @@
 	if (arg_exists(name, len, idxp, type, gen_load_outer, cctx->ctx_outer)
 									 == OK)
 	{
-	    ++*gen_load_outer;
+	    if (gen_load_outer != NULL)
+		++*gen_load_outer;
 	    return OK;
 	}
     }