diff --git a/pack-check.c b/pack-check.c
index 972916f..08a9fd8 100644
--- a/pack-check.c
+++ b/pack-check.c
@@ -8,39 +8,38 @@
 	void *index_base = p->index_base;
 	SHA_CTX ctx;
 	unsigned char sha1[20];
-	unsigned long pack_size = p->pack_size;
-	void *pack_base;
-	struct pack_header *hdr;
+	unsigned long offset = 0, pack_sig = p->pack_size - 20;
 	int nr_objects, err, i;
 
-	/* Header consistency check */
-	pack_base = use_pack(p, w_curs, 0, NULL);
-	hdr = (struct pack_header*)pack_base;
-	if (hdr->hdr_signature != htonl(PACK_SIGNATURE))
-		return error("Packfile %s signature mismatch", p->pack_name);
-	if (!pack_version_ok(hdr->hdr_version))
-		return error("Packfile version %d unsupported",
-			     ntohl(hdr->hdr_version));
-	nr_objects = ntohl(hdr->hdr_entries);
-	if (num_packed_objects(p) != nr_objects)
-		return error("Packfile claims to have %d objects, "
-			     "while idx size expects %d", nr_objects,
-			     num_packed_objects(p));
+	/* Note that the pack header checks are actually performed by
+	 * use_pack when it first opens the pack file.  If anything
+	 * goes wrong during those checks then the call will die out
+	 * immediately.
+	 */
 
 	SHA1_Init(&ctx);
-	SHA1_Update(&ctx, pack_base, pack_size - 20);
+	while (offset < pack_sig) {
+		unsigned int remaining;
+		unsigned char *in = use_pack(p, w_curs, offset, &remaining);
+		offset += remaining;
+		if (offset > pack_sig)
+			remaining -= offset - pack_sig;
+		SHA1_Update(&ctx, in, remaining);
+	}
 	SHA1_Final(sha1, &ctx);
-	if (hashcmp(sha1, (unsigned char *)pack_base + pack_size - 20))
+	if (hashcmp(sha1, use_pack(p, w_curs, pack_sig, NULL)))
 		return error("Packfile %s SHA1 mismatch with itself",
 			     p->pack_name);
 	if (hashcmp(sha1, (unsigned char *)index_base + index_size - 40))
 		return error("Packfile %s SHA1 mismatch with idx",
 			     p->pack_name);
+	unuse_pack(w_curs);
 
 	/* Make sure everything reachable from idx is valid.  Since we
 	 * have verified that nr_objects matches between idx and pack,
 	 * we do not do scan-streaming check on the pack file.
 	 */
+	nr_objects = num_packed_objects(p);
 	for (i = err = 0; i < nr_objects; i++) {
 		unsigned char sha1[20];
 		void *data;
@@ -73,15 +72,12 @@
 
 #define MAX_CHAIN 40
 
-static void show_pack_info(struct packed_git *p,
-		struct pack_window **w_curs)
+static void show_pack_info(struct packed_git *p)
 {
-	struct pack_header *hdr;
 	int nr_objects, i;
 	unsigned int chain_histogram[MAX_CHAIN];
 
-	hdr = (struct pack_header*)use_pack(p, w_curs, 0, NULL);
-	nr_objects = ntohl(hdr->hdr_entries);
+	nr_objects = num_packed_objects(p);
 	memset(chain_histogram, 0, sizeof(chain_histogram));
 
 	for (i = 0; i < nr_objects; i++) {
@@ -153,9 +149,7 @@
 		if (ret)
 			printf("%s: bad\n", p->pack_name);
 		else {
-			struct pack_window *w_curs = NULL;
-			show_pack_info(p, &w_curs);
-			unuse_pack(&w_curs);
+			show_pack_info(p);
 			printf("%s: ok\n", p->pack_name);
 		}
 	}