--- a/testing/mozharness/mozharness/mozilla/building/buildbase.py
+++ b/testing/mozharness/mozharness/mozilla/building/buildbase.py
@@ -844,16 +844,23 @@ or run without that action (ie: --no-{ac
         # as we don't always want every key below added to the same dict
         env = copy.deepcopy(
             super(BuildScript, self).query_env(**kwargs)
         )
 
         # first grab the buildid
         env['MOZ_BUILD_DATE'] = self.query_buildid()
 
+        # Set the source repository to what we're building from since
+        # the default is to query `hg paths` which isn't reliable with pooled
+        # storage
+        repo_path = self._query_repo()
+        assert repo_path
+        env['MOZ_SOURCE_REPO'] = repo_path
+
         if self.query_is_nightly() or self.query_is_nightly_promotion():
             if self.query_is_nightly():
                 # nightly promotion needs to set update_channel but not do all the 'IS_NIGHTLY'
                 # automation parts like uploading symbols for now
                 env["IS_NIGHTLY"] = "yes"
             # in branch_specifics.py we might set update_channel explicitly
             if c.get('update_channel'):
                 env["MOZ_UPDATE_CHANNEL"] = c['update_channel']