diff --git a/tracext/git/PyGIT.py b/tracext/git/PyGIT.py
index 10c6d8f..07d0c98 100644
--- a/tracext/git/PyGIT.py
+++ b/tracext/git/PyGIT.py
@@ -19,7 +19,7 @@
 import os, re, sys, time, weakref
 from collections import deque
 from functools import partial
-from threading import Lock
+from threading import Lock, RLock
 from subprocess import Popen, PIPE
 from operator import itemgetter
 import cStringIO
@@ -256,7 +256,7 @@ def __init__(self, git_dir, log, git_bin='git', git_fs_encoding=None):
 
         # caches
         self.__rev_cache = None
-        self.__rev_cache_lock = Lock()
+        self.__rev_cache_lock = RLock()
 
         # cache the last 200 commit messages
         self.__commit_msg_cache = SizedDict(200)
@@ -511,6 +511,22 @@ def verifyrev(self, rev):
                 return None
             return sha[1]
 
+        if GitCore.is_sha(rc):
+            # rev-parse returned a sha that isn't in the rev_dict or the tag_set
+            # it's possible the cache is out of date
+            with self.__rev_cache_lock:
+                # A different thread might have already refreshed cache
+                _rev_cache = self.rev_cache  # update local copy
+                if rc in _rev_cache.rev_dict:
+                    return rc
+
+                # If we've gotten here, try rebuilding the cache
+                self.__rev_cache = None
+                _rev_cache = self.rev_cache  # triggers a rebuild
+
+                if rc in _rev_cache.rev_dict:
+                    return rc
+
         return None
 
     def shortrev(self, rev, min_len=7):