diff --git a/buffer.py b/buffer.py
index c9e4e6f..ee2441a 100644
--- a/buffer.py
+++ b/buffer.py
@@ -537,7 +537,7 @@ class Binary32Buffer(FileBuffer):
         if groupdiv >= self.numgroups:
             return None
 
-        bytemod = (cx + self.bytepad) % bytespace
+        bytemod = (cx + self.bytepad - groupdiv) % bytespace
         if bytemod == 0:
             return None