diff --git a/lib/session.js b/lib/session.js
index c6bba9a6..59025af1 100644
--- a/lib/session.js
+++ b/lib/session.js
@@ -347,7 +347,8 @@ export default class Session {
     const { cli, upstream, branch } = this;
     const branchName = `${upstream}/${branch}`;
     cli.startSpinner(`Bringing ${branchName} up to date...`);
-    await runAsync('git', ['fetch', upstream, branch]);
+    const maybeUnshallow = fs.existsSync('.git/shallow') ? ['--unshallow'] : [];
+    await runAsync('git', ['fetch', ...maybeUnshallow, upstream, branch]);
     cli.stopSpinner(`${branchName} is now up-to-date`);
     const stray = this.getStrayCommits(true);
     if (!stray.length) {