diff --git a/builder.py b/builder.py
index fd5a0f3..71d539d 100644
--- a/builder.py
+++ b/builder.py
@@ -127,7 +127,8 @@ def main(targets, buildfunc):
         lock = state.Lock(t)
         lock.trylock()
         if not lock.owned:
-            log('%s (locked...)\n' % _nice(t))
+            if vars.DEBUG_LOCKS:
+                log('%s (locked...)\n' % _nice(t))
             locked.append(t)
         else:
             jwack.start_job(t, lock,
@@ -142,7 +143,8 @@ def main(targets, buildfunc):
                 lock.wait()
                 lock.trylock()
             assert(lock.owned)
-            log('%s (...unlocked!)\n' % _nice(t))
+            if vars.DEBUG_LOCKS:
+                log('%s (...unlocked!)\n' % _nice(t))
             if state.stamped(t) == None:
                 err('%s: failed in another thread\n' % _nice(t))
                 retcode[0] = 2
diff --git a/redo.py b/redo.py
index c232244..86874af 100755
--- a/redo.py
+++ b/redo.py
@@ -9,6 +9,7 @@ j,jobs=    maximum number of jobs to build at once
 d,debug    print dependency checks as they happen
 v,verbose  print commands as they are run
 shuffle    randomize the build order to find dependency bugs
+debug-locks  print messages about file locking (useful for debugging)
 """
 o = options.Options('redo', optspec)
 (opt, flags, extra) = o.parse(sys.argv[1:])
@@ -21,6 +22,8 @@ if opt.verbose:
     os.environ['REDO_VERBOSE'] = '1'
 if opt.shuffle:
     os.environ['REDO_SHUFFLE'] = '1'
+if opt.debug_locks:
+    os.environ['REDO_DEBUG_LOCKS'] = '1'
 
 is_root = not os.environ.get('REDO', '')
 
diff --git a/vars.py b/vars.py
index ae7ad0a..9c0b888 100644
--- a/vars.py
+++ b/vars.py
@@ -5,6 +5,7 @@ PWD = os.environ.get('REDO_PWD', '')
 TARGET = os.environ.get('REDO_TARGET', '')
 DEPTH = os.environ.get('REDO_DEPTH', '')
 DEBUG = atoi.atoi(os.environ.get('REDO_DEBUG', ''))
+DEBUG_LOCKS = os.environ.get('REDO_DEBUG_LOCKS', '') and 1 or 0
 VERBOSE = os.environ.get('REDO_VERBOSE', '') and 1 or 0
 SHUFFLE = os.environ.get('REDO_SHUFFLE', '') and 1 or 0
 STARTDIR = os.environ['REDO_STARTDIR']