diff -urN a/bsdiff.c b/bsdiff.c
--- a/bsdiff.c	2005-08-16 22:13:52.000000000 +0000
+++ b/bsdiff.c	2023-11-07 02:32:11.000000000 +0000
@@ -239,7 +239,7 @@
 	if (oldsize > t_off_max)
 		err(1, "file too large %s", argv[1]);
 
-	old = mmap(NULL, oldsize, PROT_READ, MAP_SHARED | MAP_POPULATE, fd, 0);
+	old = mmap(NULL, oldsize, PROT_READ, MAP_SHARED, fd, 0);
 	if (old == MAP_FAILED)
 		err(1, "mmap() %s", argv[1]);
 	close(fd);
@@ -262,7 +262,7 @@
 	if (newsize > t_off_max)
 		err(1, "file too large %s", argv[2]);
 
-	new = mmap(NULL, newsize, PROT_READ, MAP_SHARED | MAP_POPULATE, fd, 0);
+	new = mmap(NULL, newsize, PROT_READ, MAP_SHARED, fd, 0);
 	if (new == MAP_FAILED)
 		err(1, "mmap %s", argv[2]);
 	close(fd);
