diff --git a/edosl0util/eos.py b/edosl0util/eos.py
index 2174cdef624c1b7e156b837be03666c88ebb12b8..91b5fa3b5b7082cf8f3d4a480d1dd6bc389b8500 100644
--- a/edosl0util/eos.py
+++ b/edosl0util/eos.py
@@ -64,7 +64,7 @@ def _calmode(p):
 
 
 def _mirrorside(p):
-    return bytes(p.secondary_header)[8] & 0x1 + 1
+    return (bytes(p.secondary_header)[8] & 0x1) + 1
 
 
 def _scancount(p):