diff --git a/commit-graph.c b/commit-graph.c
index 6dc777e2f3..aa3adb912f 100644
--- a/commit-graph.c
+++ b/commit-graph.c
@@ -1576,7 +1576,8 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 	if (ctx->split) {
 		char *lock_name = get_chain_filename(ctx->odb);
 
-		hold_lock_file_for_update(&lk, lock_name, LOCK_DIE_ON_ERROR);
+		hold_lock_file_for_update_mode(&lk, lock_name,
+					       LOCK_DIE_ON_ERROR, 0444);
 
 		fd = git_mkstemp_mode(ctx->graph_name, 0444);
 		if (fd < 0) {
@@ -1584,9 +1585,16 @@ static int write_commit_graph_file(struct write_commit_graph_context *ctx)
 			return -1;
 		}
 
+		if (adjust_shared_perm(ctx->graph_name)) {
+			error(_("unable to adjust shared permissions for '%s'"),
+			      ctx->graph_name);
+			return -1;
+		}
+
 		f = hashfd(fd, ctx->graph_name);
 	} else {
-		hold_lock_file_for_update(&lk, ctx->graph_name, LOCK_DIE_ON_ERROR);
+		hold_lock_file_for_update_mode(&lk, ctx->graph_name,
+					       LOCK_DIE_ON_ERROR, 0444);
 		fd = lk.tempfile->fd;
 		f = hashfd(lk.tempfile->fd, lk.tempfile->filename.buf);
 	}
diff --git a/lockfile.c b/lockfile.c
index 8e8ab4f29f..cc9a4b8428 100644
--- a/lockfile.c
+++ b/lockfile.c
@@ -70,7 +70,8 @@ static void resolve_symlink(struct strbuf *path)
 }
 
 /* Make sure errno contains a meaningful value on error */
-static int lock_file(struct lock_file *lk, const char *path, int flags)
+static int lock_file(struct lock_file *lk, const char *path, int flags,
+		     int mode)
 {
 	struct strbuf filename = STRBUF_INIT;
 
@@ -79,7 +80,7 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
 		resolve_symlink(&filename);
 
 	strbuf_addstr(&filename, LOCK_SUFFIX);
-	lk->tempfile = create_tempfile(filename.buf);
+	lk->tempfile = create_tempfile_mode(filename.buf, mode);
 	strbuf_release(&filename);
 	return lk->tempfile ? lk->tempfile->fd : -1;
 }
@@ -99,7 +100,7 @@ static int lock_file(struct lock_file *lk, const char *path, int flags)
  * exactly once. If timeout_ms is -1, try indefinitely.
  */
 static int lock_file_timeout(struct lock_file *lk, const char *path,
-			     int flags, long timeout_ms)
+			     int flags, long timeout_ms, int mode)
 {
 	int n = 1;
 	int multiplier = 1;
@@ -107,7 +108,7 @@ static int lock_file_timeout(struct lock_file *lk, const char *path,
 	static int random_initialized = 0;
 
 	if (timeout_ms == 0)
-		return lock_file(lk, path, flags);
+		return lock_file(lk, path, flags, mode);
 
 	if (!random_initialized) {
 		srand((unsigned int)getpid());
@@ -121,7 +122,7 @@ static int lock_file_timeout(struct lock_file *lk, const char *path,
 		long backoff_ms, wait_ms;
 		int fd;
 
-		fd = lock_file(lk, path, flags);
+		fd = lock_file(lk, path, flags, mode);
 
 		if (fd >= 0)
 			return fd; /* success */
@@ -169,10 +170,11 @@ NORETURN void unable_to_lock_die(const char *path, int err)
 }
 
 /* This should return a meaningful errno on failure */
-int hold_lock_file_for_update_timeout(struct lock_file *lk, const char *path,
-				      int flags, long timeout_ms)
+int hold_lock_file_for_update_timeout_mode(struct lock_file *lk,
+					   const char *path, int flags,
+					   long timeout_ms, int mode)
 {
-	int fd = lock_file_timeout(lk, path, flags, timeout_ms);
+	int fd = lock_file_timeout(lk, path, flags, timeout_ms, mode);
 	if (fd < 0) {
 		if (flags & LOCK_DIE_ON_ERROR)
 			unable_to_lock_die(path, errno);
diff --git a/lockfile.h b/lockfile.h
index 9843053ce8..db93e6ba73 100644
--- a/lockfile.h
+++ b/lockfile.h
@@ -90,6 +90,15 @@
  * functions. In particular, the state diagram and the cleanup
  * machinery are all implemented in the tempfile module.
  *
+ * Permission bits
+ * ---------------
+ *
+ * If you call either `hold_lock_file_for_update_mode` or
+ * `hold_lock_file_for_update_timeout_mode`, you can specify a suggested
+ * mode for the underlying temporary file. Note that the file isn't
+ * guaranteed to have this exact mode, since it may be limited by either
+ * the umask, 'core.sharedRepository', or both. See `adjust_shared_perm`
+ * for more.
  *
  * Error handling
  * --------------
@@ -156,12 +165,20 @@ struct lock_file {
  * file descriptor for writing to it, or -1 on error. If the file is
  * currently locked, retry with quadratic backoff for at least
  * timeout_ms milliseconds. If timeout_ms is 0, try exactly once; if
- * timeout_ms is -1, retry indefinitely. The flags argument and error
- * handling are described above.
+ * timeout_ms is -1, retry indefinitely. The flags argument, error
+ * handling, and mode are described above.
  */
-int hold_lock_file_for_update_timeout(
+int hold_lock_file_for_update_timeout_mode(
 		struct lock_file *lk, const char *path,
-		int flags, long timeout_ms);
+		int flags, long timeout_ms, int mode);
+
+static inline int hold_lock_file_for_update_timeout(
+		struct lock_file *lk, const char *path,
+		int flags, long timeout_ms)
+{
+	return hold_lock_file_for_update_timeout_mode(lk, path, flags,
+						      timeout_ms, 0666);
+}
 
 /*
  * Attempt to create a lockfile for the file at `path` and return a
@@ -175,6 +192,13 @@ static inline int hold_lock_file_for_update(
 	return hold_lock_file_for_update_timeout(lk, path, flags, 0);
 }
 
+static inline int hold_lock_file_for_update_mode(
+		struct lock_file *lk, const char *path,
+		int flags, int mode)
+{
+	return hold_lock_file_for_update_timeout_mode(lk, path, flags, 0, mode);
+}
+
 /*
  * Return a nonzero value iff `lk` is currently locked.
  */
diff --git a/t/t5318-commit-graph.sh b/t/t5318-commit-graph.sh
index 39e2918a32..424599959c 100755
--- a/t/t5318-commit-graph.sh
+++ b/t/t5318-commit-graph.sh
@@ -14,6 +14,10 @@ test_expect_success 'setup full repo' '
 	test_oid_init
 '
 
+test_expect_success POSIXPERM 'tweak umask for modebit tests' '
+	umask 022
+'
+
 test_expect_success 'verify graph with no graph file' '
 	cd "$TRASH_DIRECTORY/full" &&
 	git commit-graph verify
@@ -98,6 +102,13 @@ test_expect_success 'write graph' '
 	graph_read_expect "3"
 '
 
+test_expect_success POSIXPERM 'write graph has correct permissions' '
+	test_path_is_file $objdir/info/commit-graph &&
+	echo "-r--r--r--" >expect &&
+	test_modebits $objdir/info/commit-graph >actual &&
+	test_cmp expect actual
+'
+
 graph_git_behavior 'graph exists' full commits/3 commits/1
 
 test_expect_success 'Add more commits' '
@@ -423,7 +434,8 @@ GRAPH_BYTE_FOOTER=$(($GRAPH_OCTOPUS_DATA_OFFSET + 4 * $NUM_OCTOPUS_EDGES))
 corrupt_graph_setup() {
 	cd "$TRASH_DIRECTORY/full" &&
 	test_when_finished mv commit-graph-backup $objdir/info/commit-graph &&
-	cp $objdir/info/commit-graph commit-graph-backup
+	cp $objdir/info/commit-graph commit-graph-backup &&
+	chmod u+w $objdir/info/commit-graph
 }
 
 corrupt_graph_verify() {
@@ -437,6 +449,7 @@ corrupt_graph_verify() {
 	fi &&
 	git status --short &&
 	GIT_TEST_COMMIT_GRAPH_DIE_ON_LOAD=true git commit-graph write &&
+	chmod u+w $objdir/info/commit-graph &&
 	git commit-graph verify
 }
 
diff --git a/t/t5324-split-commit-graph.sh b/t/t5324-split-commit-graph.sh
index 594edb7307..269d0964a3 100755
--- a/t/t5324-split-commit-graph.sh
+++ b/t/t5324-split-commit-graph.sh
@@ -37,6 +37,10 @@ graph_read_expect() {
 	test_cmp expect output
 }
 
+test_expect_success POSIXPERM 'tweak umask for modebit tests' '
+	umask 022
+'
+
 test_expect_success 'create commits and write commit-graph' '
 	for i in $(test_seq 3)
 	do
@@ -401,4 +405,24 @@ test_expect_success ULIMIT_FILE_DESCRIPTORS 'handles file descriptor exhaustion'
 	)
 '
 
+while read mode modebits
+do
+	test_expect_success POSIXPERM "split commit-graph respects core.sharedrepository $mode" '
+		rm -rf $graphdir $infodir/commit-graph &&
+		git reset --hard commits/1 &&
+		test_config core.sharedrepository "$mode" &&
+		git commit-graph write --split --reachable &&
+		ls $graphdir/graph-*.graph >graph-files &&
+		test_line_count = 1 graph-files &&
+		echo "$modebits" >expect &&
+		test_modebits $graphdir/graph-*.graph >actual &&
+		test_cmp expect actual &&
+		test_modebits $graphdir/commit-graph-chain >actual &&
+		test_cmp expect actual
+	'
+done <<\EOF
+0666 -r--r--r--
+0600 -r--------
+EOF
+
 test_done
diff --git a/t/t6600-test-reach.sh b/t/t6600-test-reach.sh
index b24d850036..475564bee7 100755
--- a/t/t6600-test-reach.sh
+++ b/t/t6600-test-reach.sh
@@ -51,8 +51,10 @@ test_expect_success 'setup' '
 	done &&
 	git commit-graph write --reachable &&
 	mv .git/objects/info/commit-graph commit-graph-full &&
+	chmod u+w commit-graph-full &&
 	git show-ref -s commit-5-5 | git commit-graph write --stdin-commits &&
 	mv .git/objects/info/commit-graph commit-graph-half &&
+	chmod u+w commit-graph-half &&
 	git config core.commitGraph true
 '
 
diff --git a/tempfile.c b/tempfile.c
index d43ad8c191..94aa18f3f7 100644
--- a/tempfile.c
+++ b/tempfile.c
@@ -130,17 +130,17 @@ static void deactivate_tempfile(struct tempfile *tempfile)
 }
 
 /* Make sure errno contains a meaningful value on error */
-struct tempfile *create_tempfile(const char *path)
+struct tempfile *create_tempfile_mode(const char *path, int mode)
 {
 	struct tempfile *tempfile = new_tempfile();
 
 	strbuf_add_absolute_path(&tempfile->filename, path);
 	tempfile->fd = open(tempfile->filename.buf,
-			    O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, 0666);
+			    O_RDWR | O_CREAT | O_EXCL | O_CLOEXEC, mode);
 	if (O_CLOEXEC && tempfile->fd < 0 && errno == EINVAL)
 		/* Try again w/o O_CLOEXEC: the kernel might not support it */
 		tempfile->fd = open(tempfile->filename.buf,
-				    O_RDWR | O_CREAT | O_EXCL, 0666);
+				    O_RDWR | O_CREAT | O_EXCL, mode);
 	if (tempfile->fd < 0) {
 		deactivate_tempfile(tempfile);
 		return NULL;
diff --git a/tempfile.h b/tempfile.h
index cddda0a33c..4de3bc77d2 100644
--- a/tempfile.h
+++ b/tempfile.h
@@ -88,8 +88,16 @@ struct tempfile {
  * Attempt to create a temporary file at the specified `path`. Return
  * a tempfile (whose "fd" member can be used for writing to it), or
  * NULL on error. It is an error if a file already exists at that path.
+ * Note that `mode` will be further modified by the umask, and possibly
+ * `core.sharedRepository`, so it is not guaranteed to have the given
+ * mode.
  */
-struct tempfile *create_tempfile(const char *path);
+struct tempfile *create_tempfile_mode(const char *path, int mode);
+
+static inline struct tempfile *create_tempfile(const char *path)
+{
+	return create_tempfile_mode(path, 0666);
+}
 
 /*
  * Register an existing file as a tempfile, meaning that it will be