diff --git a/mm/cma.c b/mm/cma.c
index 474c644..a951a3b 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -58,7 +58,9 @@
 
 static unsigned long cma_bitmap_aligned_mask(struct cma *cma, int align_order)
 {
-	return (1UL << (align_order >> cma->order_per_bit)) - 1;
+	if (align_order <= cma->order_per_bit)
+		return 0;
+	return (1UL << (align_order - cma->order_per_bit)) - 1;
 }
 
 static unsigned long cma_bitmap_maxno(struct cma *cma)