diff --git a/Test.dsk b/Test.dsk
index 4d67b11..11a9afe 100644
Binary files a/Test.dsk and b/Test.dsk differ
diff --git a/asm/prodos.fnl b/asm/prodos.fnl
index 142a95d..27b1351 100644
--- a/asm/prodos.fnl
+++ b/asm/prodos.fnl
@@ -246,7 +246,7 @@
 (fn bit-in-bytes [bytes ibit]
   (local ibyte (math.floor (/ ibit 8)))
   (local byte (string.byte (bytes:sub (+ ibyte 1) (+ ibyte 1))))
-  (local mask (bit.lshift 1 (% ibit 8)))
+  (local mask (bit.rshift 0x80 (% ibit 8)))
   (values byte mask ibyte))
 
 (fn Prodos.parse-bitmap [self]