diff --git a/hgext3rd/fbamend/hiddenoverride.py b/hgext3rd/fbamend/hiddenoverride.py
--- a/hgext3rd/fbamend/hiddenoverride.py
+++ b/hgext3rd/fbamend/hiddenoverride.py
@@ -8,7 +8,9 @@
 from __future__ import absolute_import
 
 import contextlib
+import errno
 import os
+import time
 
 from mercurial.node import short
 from mercurial import (
@@ -72,7 +74,15 @@
     return result
 
 @contextlib.contextmanager
-def flock(lockpath):
+def flock(lockpath, description, timeout=-1):
+    """A flock based lock object. Currently it is always non-blocking.
+
+    Note that since it is flock based, you can accidentally take it multiple
+    times within one process and the first one to be released will release all
+    of them. So the caller needs to be careful to not create more than one
+    instance per lock.
+    """
+
     # best effort lightweight lock
     try:
         import fcntl
@@ -80,15 +90,29 @@
     except ImportError:
         # fallback to Mercurial lock
         vfs = vfsmod.vfs(os.path.dirname(lockpath))
-        with lockmod.lock(vfs, os.path.basename(lockpath)):
+        with lockmod.lock(vfs, os.path.basename(lockpath), timeout=timeout):
             yield
         return
     # make sure lock file exists
     util.makedirs(os.path.dirname(lockpath))
     with open(lockpath, 'a'):
         pass
-    lockfd = os.open(lockpath, os.O_RDONLY | os.O_CREAT, 0o664)
-    fcntl.flock(lockfd, fcntl.LOCK_EX)
+    lockfd = os.open(lockpath, os.O_RDONLY, 0o664)
+    start = time.time()
+    while True:
+        try:
+            fcntl.flock(lockfd, fcntl.LOCK_EX | fcntl.LOCK_NB)
+            break
+        except IOError as ex:
+            if ex.errno == errno.EAGAIN:
+                if timeout != -1 and time.time() - start > timeout:
+                    raise error.LockHeld(errno.EAGAIN, lockpath, description,
+                                         '')
+                else:
+                    time.sleep(0.05)
+                    continue
+            raise
+
     try:
         yield
     finally:
@@ -97,7 +121,7 @@
 
 def savepinnednodes(repo, newpin, newunpin, fullargs):
     # take a narrowed lock so it does not affect repo lock
-    with flock(repo.svfs.join('obsinhibit.lock')):
+    with flock(repo.svfs.join('obsinhibit.lock'), 'save pinned nodes'):
         orignodes = loadpinnednodes(repo)
         nodes = set(orignodes)
         nodes |= set(newpin)