diff --git a/gclient_scm.py b/gclient_scm.py
index 007c5164d..a10a56d21 100644
--- a/gclient_scm.py
+++ b/gclient_scm.py
@@ -1259,10 +1259,18 @@ class GitWrapper(SCMWrapper):
     return branch
 
   def _Capture(self, args, **kwargs):
+    set_git_dir = 'cwd' not in kwargs
     kwargs.setdefault('cwd', self.checkout_path)
     kwargs.setdefault('stderr', subprocess2.PIPE)
     strip = kwargs.pop('strip', True)
     env = scm.GIT.ApplyEnvVars(kwargs)
+    # If an explicit cwd isn't set, then default to the .git/ subdir so we get
+    # stricter behavior.  This can be useful in cases of slight corruption --
+    # we don't accidentally go corrupting parent git checks too.  See
+    # https://crbug.com/1000825 for an example.
+    if set_git_dir:
+      env.setdefault('GIT_DIR', os.path.abspath(os.path.join(
+          self.checkout_path, '.git')))
     ret = subprocess2.check_output(
         ['git'] + args, env=env, **kwargs).decode('utf-8')
     if strip: