diff --git a/i3pystatus/mail/__init__.py b/i3pystatus/mail/__init__.py
index e683f0e..330494c 100644
--- a/i3pystatus/mail/__init__.py
+++ b/i3pystatus/mail/__init__.py
@@ -43,6 +43,10 @@ class Mail(IntervalModule):
             pass
 
     def run(self):
+        """
+        Returns the sum of unread messages across all registered backends
+        """
+
         unread = sum(map(lambda backend: backend.unread, self.backends))
 
         if not unread:
diff --git a/i3pystatus/mail/notmuchmail.py b/i3pystatus/mail/notmuchmail.py
index 3919d45..bd3ffe3 100644
--- a/i3pystatus/mail/notmuchmail.py
+++ b/i3pystatus/mail/notmuchmail.py
@@ -38,7 +38,9 @@ class Notmuch(Backend):
     @property
     def unread(self):
         db = notmuch.Database(self.db_path)
-        return notmuch.Query(db, "tag:unread and tag:inbox").count_messages()
+        result = notmuch.Query(db, "tag:unread and tag:inbox").count_messages()
+        db.close()
+        return result
 
 
 Backend = Notmuch