diff --git a/src/os_mac_conv.c b/src/os_mac_conv.c
index fd62124..734f8f6 100644
--- a/src/os_mac_conv.c
+++ b/src/os_mac_conv.c
@@ -570,12 +570,17 @@
 {
     if (mch_getenv((char_u *)"LANG") == NULL)
     {
-	char	buf[20];
+	char	buf[50];
+
+	// $LANG is not set, either because it was unset or Vim was started
+	// from the Dock.  Query the system locale.
 	if (LocaleRefGetPartString(NULL,
 		    kLocaleLanguageMask | kLocaleLanguageVariantMask |
 		    kLocaleRegionMask | kLocaleRegionVariantMask,
-		    sizeof buf, buf) == noErr && *buf)
+		    sizeof(buf) - 10, buf) == noErr && *buf)
 	{
+	    if (strcasestr(buf, "utf-8") == NULL)
+		strcat(buf, ".UTF-8");
 	    vim_setenv((char_u *)"LANG", (char_u *)buf);
 #   ifdef HAVE_LOCALE_H
 	    setlocale(LC_ALL, "");