diff --git a/ds/bitmap.c b/ds/bitmap.c
index 064d10c..514be59 100644
--- a/ds/bitmap.c
+++ b/ds/bitmap.c
@@ -25,7 +25,7 @@ void bitmap_set(unsigned long *map, unsigned long bit)
 void bitmap_clear(unsigned long *map, unsigned long bit)
 {
 	unsigned long index = bit / BITS_PER_WORD;
-	unsigned long offset = bit & (BITS_PER_WORD - 1);
+	unsigned long offset = (BITS_PER_WORD - bit - 1) & (BITS_PER_WORD - 1);
 	unsigned long mask = 1ul << offset;
 
 	map[index] &= ~mask;