diff --git a/injector_test.py b/injector_test.py
index 0a00e94..1f835eb 100644
--- a/injector_test.py
+++ b/injector_test.py
@@ -782,8 +782,10 @@ def test_assisted_builder_injection_uses_the_same_binding_key_every_time():
 
 class TestThreadSafety(object):
     def setup(self):
+        self.event = threading.Event()
+
         def configure(binder):
-            binder.bind(str, to=lambda: sleep(1) and 'this is str')
+            binder.bind(str, to=lambda: self.event.wait() and 'this is str')
 
         class XXX(object):
             @inject(s=str)
@@ -807,6 +809,8 @@ class TestThreadSafety(object):
         for t in threads:
             t.start()
 
+        self.event.set()
+
         for t in threads:
             t.join()