diff --git a/git_cache.py b/git_cache.py
index 6554da8d7..0dc40e38c 100755
--- a/git_cache.py
+++ b/git_cache.py
@@ -357,15 +357,12 @@ class Mirror(object):
     """
     if not self.bootstrap_bucket:
       return False
-    python_fallback = False
-    if (sys.platform.startswith('win') and
-        not gclient_utils.FindExecutable('7z')):
-      python_fallback = True
-    elif sys.platform.startswith('darwin'):
-      # The OSX version of unzip doesn't support zip64.
-      python_fallback = True
-    elif not gclient_utils.FindExecutable('unzip'):
-      python_fallback = True
+    python_fallback = (
+        (sys.platform.startswith('win') and
+          not gclient_utils.FindExecutable('7z')) or
+        (not gclient_utils.FindExecutable('unzip')) or
+        ('ZIP64_SUPPORT' not in subprocess.check_output(["unzip", "-v"]))
+    )
 
     gs_folder = 'gs://%s/%s' % (self.bootstrap_bucket, self.basedir)
     gsutil = Gsutil(self.gsutil_exe, boto_path=None)