diff --git a/mm/readahead.c b/mm/readahead.c
index 50241836fe82d8d986e458172f13d8d8f2bb2f62..7cdbb44aa90bd99bef05f43ee27cc13b2121ed7a 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -401,6 +401,7 @@ ondemand_readahead(struct address_space *mapping,
 		   unsigned long req_size)
 {
 	unsigned long max = max_sane_readahead(ra->ra_pages);
+	pgoff_t prev_offset;
 
 	/*
 	 * start of file
@@ -452,8 +453,11 @@ ondemand_readahead(struct address_space *mapping,
 
 	/*
 	 * sequential cache miss
+	 * trivial case: (offset - prev_offset) == 1
+	 * unaligned reads: (offset - prev_offset) == 0
 	 */
-	if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 1UL)
+	prev_offset = (unsigned long long)ra->prev_pos >> PAGE_CACHE_SHIFT;
+	if (offset - prev_offset <= 1UL)
 		goto initial_readahead;
 
 	/*