diff --git a/lib/pack.js b/lib/pack.js
index 568345392c4..b6a08d86506 100644
--- a/lib/pack.js
+++ b/lib/pack.js
@@ -120,7 +120,9 @@ function packDirectory (mani, dir, target) {
         cwd: dir,
         prefix: 'package/',
         portable: true,
-        noMtime: true,
+        // Provide a specific date in the 1980s for the benefit of zip,
+        // which is confounded by files dated at the Unix epoch 0.
+        mtime: new Date('1985-10-26T08:15:00.000Z'),
         gzip: true
       }