diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 7025c32fbb..6ffbb7ce35 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -380,16 +380,18 @@ static const char *open_pack_file(const char *pack_name)
 
 static void parse_pack_header(void)
 {
-	struct pack_header *hdr = fill(sizeof(struct pack_header));
+	unsigned char *hdr = fill(sizeof(struct pack_header));
 
 	/* Header consistency check */
-	if (hdr->hdr_signature != htonl(PACK_SIGNATURE))
+	if (get_be32(hdr) != PACK_SIGNATURE)
 		die(_("pack signature mismatch"));
-	if (!pack_version_ok(hdr->hdr_version))
+	hdr += 4;
+	if (!pack_version_ok_native(get_be32(hdr)))
 		die(_("pack version %"PRIu32" unsupported"),
-			ntohl(hdr->hdr_version));
+		    get_be32(hdr));
+	hdr += 4;
 
-	nr_objects = ntohl(hdr->hdr_entries);
+	nr_objects = get_be32(hdr);
 	use(sizeof(struct pack_header));
 }
 
@@ -1956,19 +1958,11 @@ int cmd_index_pack(int argc,
 					warning(_("no threads support, ignoring %s"), arg);
 					nr_threads = 1;
 				}
-			} else if (starts_with(arg, "--pack_header=")) {
-				struct pack_header *hdr;
-				char *c;
-
-				hdr = (struct pack_header *)input_buffer;
-				hdr->hdr_signature = htonl(PACK_SIGNATURE);
-				hdr->hdr_version = htonl(strtoul(arg + 14, &c, 10));
-				if (*c != ',')
-					die(_("bad %s"), arg);
-				hdr->hdr_entries = htonl(strtoul(c + 1, &c, 10));
-				if (*c)
-					die(_("bad %s"), arg);
-				input_len = sizeof(*hdr);
+			} else if (skip_prefix(arg, "--pack_header=", &arg)) {
+				if (parse_pack_header_option(arg,
+							     input_buffer,
+							     &input_len) < 0)
+					die(_("bad --pack_header: %s"), arg);
 			} else if (!strcmp(arg, "-v")) {
 				verbose = 1;
 			} else if (!strcmp(arg, "--progress-title")) {
diff --git a/builtin/unpack-objects.c b/builtin/unpack-objects.c
index a1c28e97e7..f6b9825fb0 100644
--- a/builtin/unpack-objects.c
+++ b/builtin/unpack-objects.c
@@ -18,6 +18,7 @@
 #include "progress.h"
 #include "decorate.h"
 #include "fsck.h"
+#include "packfile.h"
 
 static int dry_run, quiet, recover, has_errors, strict;
 static const char unpack_usage[] = "git unpack-objects [-n] [-q] [-r] [--strict]";
@@ -578,15 +579,16 @@ static void unpack_one(unsigned nr)
 static void unpack_all(void)
 {
 	int i;
-	struct pack_header *hdr = fill(sizeof(struct pack_header));
+	unsigned char *hdr = fill(sizeof(struct pack_header));
 
-	nr_objects = ntohl(hdr->hdr_entries);
-
-	if (ntohl(hdr->hdr_signature) != PACK_SIGNATURE)
+	if (get_be32(hdr) != PACK_SIGNATURE)
 		die("bad pack file");
-	if (!pack_version_ok(hdr->hdr_version))
+	hdr += 4;
+	if (!pack_version_ok_native(get_be32(hdr)))
 		die("unknown pack file version %"PRIu32,
-			ntohl(hdr->hdr_version));
+		    get_be32(hdr));
+	hdr += 4;
+	nr_objects = get_be32(hdr);
 	use(sizeof(struct pack_header));
 
 	if (!quiet)
@@ -647,19 +649,10 @@ int cmd_unpack_objects(int argc,
 				fsck_set_msg_types(&fsck_options, arg);
 				continue;
 			}
-			if (starts_with(arg, "--pack_header=")) {
-				struct pack_header *hdr;
-				char *c;
-
-				hdr = (struct pack_header *)buffer;
-				hdr->hdr_signature = htonl(PACK_SIGNATURE);
-				hdr->hdr_version = htonl(strtoul(arg + 14, &c, 10));
-				if (*c != ',')
-					die("bad %s", arg);
-				hdr->hdr_entries = htonl(strtoul(c + 1, &c, 10));
-				if (*c)
-					die("bad %s", arg);
-				len = sizeof(*hdr);
+			if (skip_prefix(arg, "--pack_header=", &arg)) {
+				if (parse_pack_header_option(arg,
+							     buffer, &len) < 0)
+					die(_("bad --pack_header: %s"), arg);
 				continue;
 			}
 			if (skip_prefix(arg, "--max-input-size=", &arg)) {
diff --git a/compat/bswap.h b/compat/bswap.h
index 512f6f4b99..b34054f2bd 100644
--- a/compat/bswap.h
+++ b/compat/bswap.h
@@ -171,23 +171,23 @@ static inline uint64_t get_be64(const void *ptr)
 static inline void put_be32(void *ptr, uint32_t value)
 {
 	unsigned char *p = ptr;
-	p[0] = value >> 24;
-	p[1] = value >> 16;
-	p[2] = value >>  8;
-	p[3] = value >>  0;
+	p[0] = (value >> 24) & 0xff;
+	p[1] = (value >> 16) & 0xff;
+	p[2] = (value >>  8) & 0xff;
+	p[3] = (value >>  0) & 0xff;
 }
 
 static inline void put_be64(void *ptr, uint64_t value)
 {
 	unsigned char *p = ptr;
-	p[0] = value >> 56;
-	p[1] = value >> 48;
-	p[2] = value >> 40;
-	p[3] = value >> 32;
-	p[4] = value >> 24;
-	p[5] = value >> 16;
-	p[6] = value >>  8;
-	p[7] = value >>  0;
+	p[0] = (value >> 56) & 0xff;
+	p[1] = (value >> 48) & 0xff;
+	p[2] = (value >> 40) & 0xff;
+	p[3] = (value >> 32) & 0xff;
+	p[4] = (value >> 24) & 0xff;
+	p[5] = (value >> 16) & 0xff;
+	p[6] = (value >>  8) & 0xff;
+	p[7] = (value >>  0) & 0xff;
 }
 
 #endif /* COMPAT_BSWAP_H */
diff --git a/pack.h b/pack.h
index a8da040629..78f8d8b213 100644
--- a/pack.h
+++ b/pack.h
@@ -13,7 +13,8 @@ struct repository;
  */
 #define PACK_SIGNATURE 0x5041434b	/* "PACK" */
 #define PACK_VERSION 2
-#define pack_version_ok(v) ((v) == htonl(2) || (v) == htonl(3))
+#define pack_version_ok(v) pack_version_ok_native(ntohl(v))
+#define pack_version_ok_native(v) ((v) == 2 || (v) == 3)
 struct pack_header {
 	uint32_t hdr_signature;
 	uint32_t hdr_version;
diff --git a/packfile.c b/packfile.c
index cc7ab6403a..2d80d80cb3 100644
--- a/packfile.c
+++ b/packfile.c
@@ -2315,3 +2315,23 @@ int is_promisor_object(struct repository *r, const struct object_id *oid)
 	}
 	return oidset_contains(&promisor_objects, oid);
 }
+
+int parse_pack_header_option(const char *in, unsigned char *out, unsigned int *len)
+{
+	unsigned char *hdr;
+	char *c;
+
+	hdr = out;
+	put_be32(hdr, PACK_SIGNATURE);
+	hdr += 4;
+	put_be32(hdr, strtoul(in, &c, 10));
+	hdr += 4;
+	if (*c != ',')
+		return -1;
+	put_be32(hdr, strtoul(c + 1, &c, 10));
+	hdr += 4;
+	if (*c)
+		return -1;
+	*len = hdr - out;
+	return 0;
+}
diff --git a/packfile.h b/packfile.h
index 58104fa009..00ada7a938 100644
--- a/packfile.h
+++ b/packfile.h
@@ -216,4 +216,10 @@ int is_promisor_object(struct repository *r, const struct object_id *oid);
 int load_idx(const char *path, const unsigned int hashsz, void *idx_map,
 	     size_t idx_size, struct packed_git *p);
 
+/*
+ * Parse a --pack_header option as accepted by index-pack and unpack-objects,
+ * turning it into the matching bytes we'd find in a pack.
+ */
+int parse_pack_header_option(const char *in, unsigned char *out, unsigned int *len);
+
 #endif