diff --git a/dataset/persistence/database.py b/dataset/persistence/database.py
index d87963a..3a5f18f 100644
--- a/dataset/persistence/database.py
+++ b/dataset/persistence/database.py
@@ -80,7 +80,7 @@ class Database(object):
             self.local.must_release = True
 
     def _release_internal(self):
-        if not hasattr(self.local, 'must_release') and self.local.must_release:
+        if getattr(self.local, 'must_release', None):
             self.lock.release()
             self.local.must_release = False
 
diff --git a/setup.py b/setup.py
index eb0c54b..ba6ed1a 100644
--- a/setup.py
+++ b/setup.py
@@ -8,7 +8,7 @@ if sys.version_info[:2] <= (2, 6):
 
 setup(
     name='dataset',
-    version='0.5.4',
+    version='0.5.5',
     description="Toolkit for Python-based data processing.",
     long_description="",
     classifiers=[