diff --git a/mercurial/hg.py b/mercurial/hg.py
--- a/mercurial/hg.py
+++ b/mercurial/hg.py
@@ -165,7 +165,7 @@ def clone(ui, source, dest=None, pull=Fa
                 # can end up with extra data in the cloned revlogs that's
                 # not pointed to by changesets, thus causing verify to
                 # fail
-                src_lock = src_repo.lock()
+                src_lock = src_repo.lock(wait=False)
             except error.LockError:
                 copy = False