diff --git a/mm/cma.c b/mm/cma.c
index 9e4549191789..c0da318c020e 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -59,7 +59,7 @@ const char *cma_get_name(const struct cma *cma)
 }
 
 static unsigned long cma_bitmap_aligned_mask(const struct cma *cma,
-					     int align_order)
+					     unsigned int align_order)
 {
 	if (align_order <= cma->order_per_bit)
 		return 0;
@@ -67,17 +67,14 @@ static unsigned long cma_bitmap_aligned_mask(const struct cma *cma,
 }
 
 /*
- * Find a PFN aligned to the specified order and return an offset represented in
- * order_per_bits.
+ * Find the offset of the base PFN from the specified align_order.
+ * The value returned is represented in order_per_bits.
  */
 static unsigned long cma_bitmap_aligned_offset(const struct cma *cma,
-					       int align_order)
+					       unsigned int align_order)
 {
-	if (align_order <= cma->order_per_bit)
-		return 0;
-
-	return (ALIGN(cma->base_pfn, (1UL << align_order))
-		- cma->base_pfn) >> cma->order_per_bit;
+	return (cma->base_pfn & ((1UL << align_order) - 1))
+		>> cma->order_per_bit;
 }
 
 static unsigned long cma_bitmap_pages_to_bits(const struct cma *cma,