diff --git a/src/eval.c b/src/eval.c
index b55ae1a..62266f8 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -695,6 +695,7 @@
     char_u	*arg;
     char_u	*name;
     char_u	*tofree = NULL;
+    int		ignore_errors;
 
     rettv->v_type = VAR_UNKNOWN;		// clear_tv() uses this
     CLEAR_FIELD(funcexe);
@@ -702,11 +703,18 @@
     funcexe.fe_lastline = curwin->w_cursor.lnum;
     funcexe.fe_evaluate = TRUE;
 
-    // The name might be "import.Func" or "Funcref".
+    // The name might be "import.Func" or "Funcref".  We don't know, we need to
+    // ignore errors for an undefined name.  But we do want errors when an
+    // autoload script has errors.  Guess that when there is a dot or '#' in
+    // the name showing errors is the right choice.
+    ignore_errors = vim_strchr(func, '.') == NULL
+				    && vim_strchr(func, AUTOLOAD_CHAR) == NULL;
     arg = func;
-    ++emsg_off;
+    if (ignore_errors)
+	++emsg_off;
     name = deref_function_name(&arg, &tofree, &EVALARG_EVALUATE, FALSE);
-    --emsg_off;
+    if (ignore_errors)
+	--emsg_off;
     if (name == NULL)
 	name = func;
 
diff --git a/src/testdir/test_cmdline.vim b/src/testdir/test_cmdline.vim
index bdcecbf..20f932b 100644
--- a/src/testdir/test_cmdline.vim
+++ b/src/testdir/test_cmdline.vim
@@ -4,6 +4,7 @@
 source screendump.vim
 source view_util.vim
 source shared.vim
+import './vim9.vim' as v9
 
 func SetUp()
   func SaveLastScreenLine()
@@ -543,6 +544,32 @@
   call assert_fails('call getcompletion("abc", [])', 'E475:')
 endfunc
 
+func Test_complete_autoload_error()
+  let save_rtp = &rtp
+  let lines =<< trim END
+      vim9script
+      export def Complete(..._): string
+        return 'match'
+      enddef
+      echo this will cause an error
+  END
+  call mkdir('Xdir/autoload', 'p')
+  call writefile(lines, 'Xdir/autoload/script.vim')
+  exe 'set rtp+=' .. getcwd() .. '/Xdir'
+
+  let lines =<< trim END
+      vim9script
+      import autoload 'script.vim'
+      command -nargs=* -complete=custom,script.Complete Cmd eval 0 + 0
+      &wildcharm = char2nr("\<Tab>")
+      feedkeys(":Cmd \<Tab>", 'xt')
+  END
+  call v9.CheckScriptFailure(lines, 'E121: Undefined variable: this')
+
+  let &rtp = save_rtp
+  call delete('Xdir', 'rf')
+endfunc
+
 func Test_fullcommand()
   let tests = {
         \ '':           '',
@@ -2671,8 +2698,7 @@
   endfunc
   set wildoptions=fuzzy
   call feedkeys(":call sendmail\<C-A>\<C-B>\"\<CR>", 'tx')
-  call assert_equal('"call SendSomemail() S1e2n3dmail() '
-        \ .. expand("<SID>") .. 'Sendmail()', @:)
+  call assert_match('"call SendSomemail() S1e2n3dmail() <SNR>\d\+_Sendmail()', @:)
   set wildoptions&
   delfunc s:Sendmail
   delfunc SendSomemail
diff --git a/src/version.c b/src/version.c
index ba0058b..4c6920f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4578,
+/**/
     4577,
 /**/
     4576,