diff --git a/setup.py b/setup.py
index 94e72b80f5e6..3723910f8356 100755
--- a/setup.py
+++ b/setup.py
@@ -79,7 +79,9 @@ def _minimal_ext_cmd(cmd):
         return out
 
     try:
-        out = _minimal_ext_cmd(['git', 'rev-parse', 'HEAD'])
+        cwd = os.getcwd()
+        git_dir = os.path.join(cwd, ".git")
+        out = _minimal_ext_cmd(['git', '--git-dir', git_dir, 'rev-parse', 'HEAD'])
         GIT_REVISION = out.strip().decode('ascii')[:7]
 
         # We need a version number that's regularly incrementing for newer commits,