--- a/xpcom/tests/moz.build
+++ b/xpcom/tests/moz.build
@@ -101,17 +101,17 @@ if CONFIG['MOZ_MEMORY']:
 #    'TestAtoms',
 #]
 
 # FIXME: bug 577500 TestStaticAtoms fails when run in dist/bin
 #CPP_UNIT_TESTS += [
 #    'TestStaticAtoms',
 #]
 
-if CONFIG['MOZ_DEBUG'] and CONFIG['OS_ARCH'] not in ('WINNT', 'Darwin'):
+if CONFIG['MOZ_DEBUG'] and CONFIG['OS_ARCH'] not in ('WINNT'):
     # FIXME bug 523392: TestDeadlockDetector doesn't like Windows
     # FIXME bug 523378: also fails on OS X
     CPP_UNIT_TESTS += [
         'TestDeadlockDetector',
         'TestDeadlockDetectorScalability',
     ]
 
 SOURCES += sorted('%s.cpp' % t for t in CPP_UNIT_TESTS)