diff --git a/swarm/manager.py b/swarm/manager.py
index 43de053..a31a1cb 100644
--- a/swarm/manager.py
+++ b/swarm/manager.py
@@ -277,7 +277,7 @@ class Manager:
         self.last_update = timestamp
 
         self.bits_toggled_on += len(bits_on)
-        self.bits_toggled_off = len(bits_off)
+        self.bits_toggled_off += len(bits_off)
 
         for ndx in bits_on:
             byte, bit = ndx >> 3, ndx & 7