diff --git a/tools/latency.py b/tools/latency.py
index 761671c11..3249e6fd1 100755
--- a/tools/latency.py
+++ b/tools/latency.py
@@ -81,7 +81,7 @@ class SBusFrame:
         return value
 
     def is_lost(self):
-        return self.byte(23) != 0
+        return self.byte(23) & 0x04
 
     def __str__(self):
         return "%.03fms " % self.start() + " ".join(["%02X" % self.byte(i) for i in range(25)])