diff --git a/go/download/_download.php b/go/download/_download.php
index 5517fef5..8fc6d356 100644
--- a/go/download/_download.php
+++ b/go/download/_download.php
@@ -1,4 +1,24 @@
 <?php
+/**
+ *
+ * Provide static links to executable downloads of Keyman products on various
+ * platforms.
+ *
+ * Usage:
+ * https://keyman.com/go/download/<PRODUCT>[?tier=<TIER>][&version=<VERSION>]
+ *
+ * PRODUCT: kmcomp|keyman-developer|keyman-windows|keyman-mac
+ * TIER: alpha|beta|stable (default 'stable')
+ * VERSION: any valid version number (default to latest for tier)
+ *
+ * Redirects to the referenced executable, e.g. keyman-18.0.252.dmg for Mac.
+ *
+ * This page is referenced by Keyman Developer Server, e.g.
+ * /go/download/keyman-mac and by Keyman Developer kmc documentation
+ * /go/download/kmcomp. These paths are rewritten by .htaccess to call into
+ * _download.php.
+ */
+
   require_once _KEYMANCOM_INCLUDES . '/autoload.php';
   use Keyman\Site\com\keyman\KeymanComSentry;
   use Keyman\Site\Common\KeymanHosts;
@@ -34,11 +54,14 @@
     $MAC_VERSION = $versions->mac->$TIER->version;
   }
 
+  // epic/mac-config changes the mac installer from a .dmg to .pkg, in version 19.0.291-alpha
+  $MAC_FILENAME = version_compare($MAC_VERSION, "19.0.291") >= 0 ? "keyman-$MAC_VERSION.pkg" : "keyman-$MAC_VERSION.dmg";
+
   $packages = [
     "kmcomp" => ["developer", $DEVELOPER_VERSION, "kmcomp-$DEVELOPER_VERSION.zip"],
     "keyman-developer" => ["developer", $DEVELOPER_VERSION, "keymandeveloper-$DEVELOPER_VERSION.exe"],
     "keyman-windows" => ["windows", $WINDOWS_VERSION, "keyman-$WINDOWS_VERSION.exe"],
-    "keyman-mac" => ["mac", $MAC_VERSION, "keyman-$MAC_VERSION.dmg"]
+    "keyman-mac" => ["mac", $MAC_VERSION, $MAC_FILENAME],
   ];
 
   if(!isset($packages[$object])) {