diff --git a/builtin/blame.c b/builtin/blame.c
index 857d98a324..b84e375b5c 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -1998,6 +1998,18 @@ static void append_merge_parents(struct commit_list **tail)
 	strbuf_release(&line);
 }
 
+/*
+ * This isn't as simple as passing sb->buf and sb->len, because we
+ * want to transfer ownership of the buffer to the commit (so we
+ * must use detach).
+ */
+static void set_commit_buffer_from_strbuf(struct commit *c, struct strbuf *sb)
+{
+	size_t len;
+	void *buf = strbuf_detach(sb, &len);
+	set_commit_buffer(c, buf, len);
+}
+
 /*
  * Prepare a dummy commit that represents the work tree (or staged) item.
  * Note that annotating work tree item never works in the reverse.
@@ -2046,7 +2058,7 @@ static struct commit *fake_working_tree_commit(struct diff_options *opt,
 		    ident, ident, path,
 		    (!contents_from ? path :
 		     (!strcmp(contents_from, "-") ? "standard input" : contents_from)));
-	set_commit_buffer(commit, strbuf_detach(&msg, NULL));
+	set_commit_buffer_from_strbuf(commit, &msg);
 
 	if (!contents_from || strcmp("-", contents_from)) {
 		struct stat st;
diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index 7ee5e08442..05d161f19f 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -289,7 +289,7 @@ static void handle_commit(struct commit *commit, struct rev_info *rev)
 	rev->diffopt.output_format = DIFF_FORMAT_CALLBACK;
 
 	parse_commit_or_die(commit);
-	commit_buffer = get_commit_buffer(commit);
+	commit_buffer = get_commit_buffer(commit, NULL);
 	author = strstr(commit_buffer, "\nauthor ");
 	if (!author)
 		die ("Could not find author in commit %s",
diff --git a/builtin/fmt-merge-msg.c b/builtin/fmt-merge-msg.c
index 01f6d59eef..ef8b254ef2 100644
--- a/builtin/fmt-merge-msg.c
+++ b/builtin/fmt-merge-msg.c
@@ -236,7 +236,7 @@ static void record_person(int which, struct string_list *people,
 	const char *field;
 
 	field = (which == 'a') ? "\nauthor " : "\ncommitter ";
-	buffer = get_commit_buffer(commit);
+	buffer = get_commit_buffer(commit, NULL);
 	name = strstr(buffer, field);
 	if (!name)
 		return;
diff --git a/builtin/index-pack.c b/builtin/index-pack.c
index 42551ce4ff..459b9f07bb 100644
--- a/builtin/index-pack.c
+++ b/builtin/index-pack.c
@@ -774,7 +774,7 @@ static void sha1_object(const void *data, struct object_entry *obj_entry,
 			}
 			if (obj->type == OBJ_COMMIT) {
 				struct commit *commit = (struct commit *) obj;
-				if (detach_commit_buffer(commit) != data)
+				if (detach_commit_buffer(commit, NULL) != data)
 					die("BUG: parse_object_buffer transmogrified our buffer");
 			}
 			obj->flags |= FLAG_CHECKED;
diff --git a/builtin/log.c b/builtin/log.c
index 2c742606bc..c599eacf72 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -919,7 +919,7 @@ static void make_cover_letter(struct rev_info *rev, int use_stdout,
 				&need_8bit_cte);
 
 	for (i = 0; !need_8bit_cte && i < nr; i++) {
-		const char *buf = get_commit_buffer(list[i]);
+		const char *buf = get_commit_buffer(list[i], NULL);
 		if (has_non_ascii(buf))
 			need_8bit_cte = 1;
 		unuse_commit_buffer(list[i], buf);
diff --git a/builtin/rev-list.c b/builtin/rev-list.c
index 3fcbf21c03..ff84a825ff 100644
--- a/builtin/rev-list.c
+++ b/builtin/rev-list.c
@@ -106,7 +106,7 @@ static void show_commit(struct commit *commit, void *data)
 	else
 		putchar('\n');
 
-	if (revs->verbose_header && get_cached_commit_buffer(commit)) {
+	if (revs->verbose_header && get_cached_commit_buffer(commit, NULL)) {
 		struct strbuf buf = STRBUF_INIT;
 		struct pretty_print_context ctx = {0};
 		ctx.abbrev = revs->abbrev;
diff --git a/commit.c b/commit.c
index e289c78327..a036e181c7 100644
--- a/commit.c
+++ b/commit.c
@@ -245,22 +245,31 @@ int unregister_shallow(const unsigned char *sha1)
 	return 0;
 }
 
-define_commit_slab(buffer_slab, void *);
+struct commit_buffer {
+	void *buffer;
+	unsigned long size;
+};
+define_commit_slab(buffer_slab, struct commit_buffer);
 static struct buffer_slab buffer_slab = COMMIT_SLAB_INIT(1, buffer_slab);
 
-void set_commit_buffer(struct commit *commit, void *buffer)
+void set_commit_buffer(struct commit *commit, void *buffer, unsigned long size)
 {
-	*buffer_slab_at(&buffer_slab, commit) = buffer;
+	struct commit_buffer *v = buffer_slab_at(&buffer_slab, commit);
+	v->buffer = buffer;
+	v->size = size;
 }
 
-const void *get_cached_commit_buffer(const struct commit *commit)
+const void *get_cached_commit_buffer(const struct commit *commit, unsigned long *sizep)
 {
-	return *buffer_slab_at(&buffer_slab, commit);
+	struct commit_buffer *v = buffer_slab_at(&buffer_slab, commit);
+	if (sizep)
+		*sizep = v->size;
+	return v->buffer;
 }
 
-const void *get_commit_buffer(const struct commit *commit)
+const void *get_commit_buffer(const struct commit *commit, unsigned long *sizep)
 {
-	const void *ret = get_cached_commit_buffer(commit);
+	const void *ret = get_cached_commit_buffer(commit, sizep);
 	if (!ret) {
 		enum object_type type;
 		unsigned long size;
@@ -271,29 +280,38 @@ const void *get_commit_buffer(const struct commit *commit)
 		if (type != OBJ_COMMIT)
 			die("expected commit for %s, got %s",
 			    sha1_to_hex(commit->object.sha1), typename(type));
+		if (sizep)
+			*sizep = size;
 	}
 	return ret;
 }
 
 void unuse_commit_buffer(const struct commit *commit, const void *buffer)
 {
-	void *cached = *buffer_slab_at(&buffer_slab, commit);
-	if (cached != buffer)
+	struct commit_buffer *v = buffer_slab_at(&buffer_slab, commit);
+	if (v->buffer != buffer)
 		free((void *)buffer);
 }
 
 void free_commit_buffer(struct commit *commit)
 {
-	void **b = buffer_slab_at(&buffer_slab, commit);
-	free(*b);
-	*b = NULL;
+	struct commit_buffer *v = buffer_slab_at(&buffer_slab, commit);
+	free(v->buffer);
+	v->buffer = NULL;
+	v->size = 0;
 }
 
-const void *detach_commit_buffer(struct commit *commit)
+const void *detach_commit_buffer(struct commit *commit, unsigned long *sizep)
 {
-	void **b = buffer_slab_at(&buffer_slab, commit);
-	void *ret = *b;
-	*b = NULL;
+	struct commit_buffer *v = buffer_slab_at(&buffer_slab, commit);
+	void *ret;
+
+	ret = v->buffer;
+	if (sizep)
+		*sizep = v->size;
+
+	v->buffer = NULL;
+	v->size = 0;
 	return ret;
 }
 
@@ -374,7 +392,7 @@ int parse_commit(struct commit *item)
 	}
 	ret = parse_commit_buffer(item, buffer, size);
 	if (save_commit_buffer && !ret) {
-		set_commit_buffer(item, buffer);
+		set_commit_buffer(item, buffer, size);
 		return 0;
 	}
 	free(buffer);
@@ -589,7 +607,7 @@ static void record_author_date(struct author_date_slab *author_date,
 			       struct commit *commit)
 {
 	const char *buf, *line_end, *ident_line;
-	const char *buffer = get_commit_buffer(commit);
+	const char *buffer = get_commit_buffer(commit, NULL);
 	struct ident_split ident;
 	char *date_end;
 	unsigned long date;
diff --git a/commit.h b/commit.h
index e1c25692f1..61559a9d45 100644
--- a/commit.h
+++ b/commit.h
@@ -54,20 +54,20 @@ void parse_commit_or_die(struct commit *item);
  * Associate an object buffer with the commit. The ownership of the
  * memory is handed over to the commit, and must be free()-able.
  */
-void set_commit_buffer(struct commit *, void *buffer);
+void set_commit_buffer(struct commit *, void *buffer, unsigned long size);
 
 /*
  * Get any cached object buffer associated with the commit. Returns NULL
  * if none. The resulting memory should not be freed.
  */
-const void *get_cached_commit_buffer(const struct commit *);
+const void *get_cached_commit_buffer(const struct commit *, unsigned long *size);
 
 /*
  * Get the commit's object contents, either from cache or by reading the object
  * from disk. The resulting memory should not be modified, and must be given
  * to unuse_commit_buffer when the caller is done.
  */
-const void *get_commit_buffer(const struct commit *);
+const void *get_commit_buffer(const struct commit *, unsigned long *size);
 
 /*
  * Tell the commit subsytem that we are done with a particular commit buffer.
@@ -86,7 +86,7 @@ void free_commit_buffer(struct commit *);
  * Disassociate any cached object buffer from the commit, but do not free it.
  * The buffer (or NULL, if none) is returned.
  */
-const void *detach_commit_buffer(struct commit *);
+const void *detach_commit_buffer(struct commit *, unsigned long *sizep);
 
 /* Find beginning and length of commit subject. */
 int find_commit_subject(const char *commit_buffer, const char **subject);
diff --git a/fsck.c b/fsck.c
index 8223780592..a7233c8d0b 100644
--- a/fsck.c
+++ b/fsck.c
@@ -339,7 +339,7 @@ static int fsck_commit_buffer(struct commit *commit, const char *buffer,
 
 static int fsck_commit(struct commit *commit, fsck_error error_func)
 {
-	const char *buffer = get_commit_buffer(commit);
+	const char *buffer = get_commit_buffer(commit, NULL);
 	int ret = fsck_commit_buffer(commit, buffer, error_func);
 	unuse_commit_buffer(commit, buffer);
 	return ret;
diff --git a/log-tree.c b/log-tree.c
index e9ef8abd37..444702163a 100644
--- a/log-tree.c
+++ b/log-tree.c
@@ -588,7 +588,7 @@ void show_log(struct rev_info *opt)
 		show_mergetag(opt, commit);
 	}
 
-	if (!get_cached_commit_buffer(commit))
+	if (!get_cached_commit_buffer(commit, NULL))
 		return;
 
 	if (opt->show_notes) {
diff --git a/merge-recursive.c b/merge-recursive.c
index 78908aaacc..a9ab328923 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -190,7 +190,7 @@ static void output_commit_title(struct merge_options *o, struct commit *commit)
 			printf(_("(bad commit)\n"));
 		else {
 			const char *title;
-			const char *msg = get_commit_buffer(commit);
+			const char *msg = get_commit_buffer(commit, NULL);
 			int len = find_commit_subject(msg, &title);
 			if (len)
 				printf("%.*s\n", len, title);
diff --git a/notes-merge.c b/notes-merge.c
index e804db2d02..fd5fae255d 100644
--- a/notes-merge.c
+++ b/notes-merge.c
@@ -672,7 +672,7 @@ int notes_merge_commit(struct notes_merge_options *o,
 	DIR *dir;
 	struct dirent *e;
 	struct strbuf path = STRBUF_INIT;
-	const char *buffer = get_commit_buffer(partial_commit);
+	const char *buffer = get_commit_buffer(partial_commit, NULL);
 	const char *msg = strstr(buffer, "\n\n");
 	int baselen;
 
diff --git a/object.c b/object.c
index 67b6e3533d..9c31e9a5e0 100644
--- a/object.c
+++ b/object.c
@@ -197,8 +197,8 @@ struct object *parse_object_buffer(const unsigned char *sha1, enum object_type t
 		if (commit) {
 			if (parse_commit_buffer(commit, buffer, size))
 				return NULL;
-			if (!get_cached_commit_buffer(commit)) {
-				set_commit_buffer(commit, buffer);
+			if (!get_cached_commit_buffer(commit, NULL)) {
+				set_commit_buffer(commit, buffer, size);
 				*eaten_p = 1;
 			}
 			obj = &commit->object;
diff --git a/pretty.c b/pretty.c
index 915bd1e2e9..b9fceedbb9 100644
--- a/pretty.c
+++ b/pretty.c
@@ -613,7 +613,7 @@ const char *logmsg_reencode(const struct commit *commit,
 	static const char *utf8 = "UTF-8";
 	const char *use_encoding;
 	char *encoding;
-	const char *msg = get_commit_buffer(commit);
+	const char *msg = get_commit_buffer(commit, NULL);
 	char *out;
 
 	if (!output_encoding || !*output_encoding) {
@@ -642,7 +642,7 @@ const char *logmsg_reencode(const struct commit *commit,
 		 * the cached copy from get_commit_buffer, we need to duplicate it
 		 * to avoid munging the cached copy.
 		 */
-		if (msg == get_cached_commit_buffer(commit))
+		if (msg == get_cached_commit_buffer(commit, NULL))
 			out = xstrdup(msg);
 		else
 			out = (char *)msg;
diff --git a/sequencer.c b/sequencer.c
index 69bcf3d801..bbaddcb05a 100644
--- a/sequencer.c
+++ b/sequencer.c
@@ -662,7 +662,7 @@ static int format_todo(struct strbuf *buf, struct commit_list *todo_list,
 	int subject_len;
 
 	for (cur = todo_list; cur; cur = cur->next) {
-		const char *commit_buffer = get_commit_buffer(cur->item);
+		const char *commit_buffer = get_commit_buffer(cur->item, NULL);
 		sha1_abbrev = find_unique_abbrev(cur->item->object.sha1, DEFAULT_ABBREV);
 		subject_len = find_commit_subject(commit_buffer, &subject);
 		strbuf_addf(buf, "%s %s %.*s\n", action_str, sha1_abbrev,
diff --git a/sha1_name.c b/sha1_name.c
index 0a65d234de..c2c938c4e1 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -869,7 +869,7 @@ static int get_sha1_oneline(const char *prefix, unsigned char *sha1,
 		commit = pop_most_recent_commit(&list, ONELINE_SEEN);
 		if (!parse_object(commit->object.sha1))
 			continue;
-		buf = get_commit_buffer(commit);
+		buf = get_commit_buffer(commit, NULL);
 		p = strstr(buf, "\n\n");
 		matches = p && !regexec(&regex, p + 2, 0, NULL, 0);
 		unuse_commit_buffer(commit, buf);