confirmed we can get this to trigger if we apply heisenbug compensation

1 files changed, 2 insertions, 4 deletions

diff --git a/lib/sqlalchemy/event.py b/lib/sqlalchemy/event.py
index f9fbcc118..603aaf383 100644
--- a/lib/sqlalchemy/event.py
+++ b/lib/sqlalchemy/event.py
@@ -146,10 +146,8 @@ class Listeners(_ExecEvent):
         return bool(self.listeners or self.parent_listeners)
         
     def append(self, obj, target):
-        # this will be needed, but not 
-        # sure why we don't seem to need it yet
- #       if obj not in self.listeners:
-        self.listeners.append(obj)
+        if obj not in self.listeners:
+            self.listeners.append(obj)
 
 class dispatcher(object):
     def __init__(self, events):