diff --git a/lib/bullet/registry/call_stack.rb b/lib/bullet/registry/call_stack.rb
index ee32b748..8a4c1b14 100644
--- a/lib/bullet/registry/call_stack.rb
+++ b/lib/bullet/registry/call_stack.rb
@@ -5,7 +5,7 @@ module Registry
     class CallStack < Base
       # remembers found association backtrace
       def add(key)
-        @registry[key] = Thread.current.backtrace
+        @registry[key] ||= Thread.current.backtrace
       end
     end
   end