diff --git a/bitmap.c b/bitmap.c
index 103706b..c27688c 100644
--- a/bitmap.c
+++ b/bitmap.c
@@ -132,7 +132,7 @@ bitmap_info_t *bitmap_fd_read(int fd, int brief)
 	void *buf;
 	unsigned int n, skip;
 
-	if (posix_memalign(&buf, 512, 8192) != 0) {
+	if (posix_memalign(&buf, 4096, 8192) != 0) {
 		fprintf(stderr, Name ": failed to allocate 8192 bytes\n");
 		return NULL;
 	}
diff --git a/super-gpt.c b/super-gpt.c
index b8c9aae..75269bf 100644
--- a/super-gpt.c
+++ b/super-gpt.c
@@ -76,7 +76,7 @@ static int load_gpt(struct supertype *st, int fd, char *devname)
 
 	free_gpt(st);
 
-	if (posix_memalign((void**)&super, 512, 32*512) != 0) {
+	if (posix_memalign((void**)&super, 4096, 32*512) != 0) {
 		fprintf(stderr, Name ": %s could not allocate superblock\n",
 			__func__);
 		return 1;