diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index 7e3fd29..cb64376 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -1455,6 +1455,23 @@
   bw!
   delfunc s:CompleteFunc3
 
+  " In Vim9 script s: can be omitted
+  let lines =<< trim END
+      vim9script
+      var CompleteFunc4Args = []
+      def CompleteFunc4(findstart: bool, base: string): any
+        add(CompleteFunc4Args, [findstart, base])
+        return findstart ? 0 : []
+      enddef
+      set completefunc=CompleteFunc4
+      new
+      setline(1, 'script1')
+      feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
+      assert_equal([[1, ''], [0, 'script1']], CompleteFunc4Args)
+      bw!
+  END
+  call v9.CheckScriptSuccess(lines)
+
   " invalid return value
   let &completefunc = {a -> 'abc'}
   call feedkeys("A\<C-X>\<C-U>\<Esc>", 'x')
diff --git a/src/userfunc.c b/src/userfunc.c
index 10a529e..696320c 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -4024,16 +4024,29 @@
 get_scriptlocal_funcname(char_u *funcname)
 {
     char	sid_buf[25];
-    int		off;
+    int		off = *funcname == 's' ? 2 : 5;
     char_u	*newname;
+    char_u	*p = funcname;
 
     if (funcname == NULL)
 	return NULL;
 
     if (STRNCMP(funcname, "s:", 2) != 0
 		&& STRNCMP(funcname, "<SID>", 5) != 0)
-	// The function name is not a script-local function name
-	return NULL;
+    {
+	ufunc_T	    *ufunc;
+
+	// The function name does not have a script-local prefix.  Try finding
+	// it when in a Vim9 script and there is no "g:" prefix.
+	if (!in_vim9script() || STRNCMP(funcname, "g:", 2) == 0)
+	    return NULL;
+	ufunc = find_func(funcname, FALSE);
+	if (ufunc == NULL || func_is_global(ufunc)
+			      || (p = vim_strchr(ufunc->uf_name, '_')) == NULL)
+	    return NULL;
+	++p;
+	off = 0;
+    }
 
     if (!SCRIPT_ID_VALID(current_sctx.sc_sid))
     {
@@ -4043,12 +4056,11 @@
     // Expand s: prefix into <SNR>nr_<name>
     vim_snprintf(sid_buf, sizeof(sid_buf), "<SNR>%ld_",
 	    (long)current_sctx.sc_sid);
-    off = *funcname == 's' ? 2 : 5;
-    newname = alloc(STRLEN(sid_buf) + STRLEN(funcname + off) + 1);
+    newname = alloc(STRLEN(sid_buf) + STRLEN(p + off) + 1);
     if (newname == NULL)
 	return NULL;
     STRCPY(newname, sid_buf);
-    STRCAT(newname, funcname + off);
+    STRCAT(newname, p + off);
 
     return newname;
 }
diff --git a/src/version.c b/src/version.c
index f313448..c996812 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4416,
+/**/
     4415,
 /**/
     4414,