diff --git a/read-cache.c b/read-cache.c
index 3c4354ee21..2121b6e7bb 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2431,6 +2431,14 @@ static int write_shared_index(struct index_state *istate,
 		delete_tempfile(&temporary_sharedindex);
 		return ret;
 	}
+	ret = adjust_shared_perm(get_tempfile_path(&temporary_sharedindex));
+	if (ret) {
+		int save_errno = errno;
+		error("cannot fix permission bits on %s", get_tempfile_path(&temporary_sharedindex));
+		delete_tempfile(&temporary_sharedindex);
+		errno = save_errno;
+		return ret;
+	}
 	ret = rename_tempfile(&temporary_sharedindex,
 			      git_path("sharedindex.%s", sha1_to_hex(si->base->sha1)));
 	if (!ret) {
diff --git a/t/t1301-shared-repo.sh b/t/t1301-shared-repo.sh
index 1312004f8c..dfece751b5 100755
--- a/t/t1301-shared-repo.sh
+++ b/t/t1301-shared-repo.sh
@@ -19,10 +19,6 @@ test_expect_success 'shared = 0400 (faulty permission u-w)' '
 	)
 '
 
-modebits () {
-	ls -l "$1" | sed -e 's|^\(..........\).*|\1|'
-}
-
 for u in 002 022
 do
 	test_expect_success POSIXPERM "shared=1 does not clear bits preset by umask $u" '
@@ -88,7 +84,7 @@ do
 
 		rm -f .git/info/refs &&
 		git update-server-info &&
-		actual="$(modebits .git/info/refs)" &&
+		actual="$(test_modebits .git/info/refs)" &&
 		verbose test "x$actual" = "x-$y"
 
 	'
@@ -98,7 +94,7 @@ do
 
 		rm -f .git/info/refs &&
 		git update-server-info &&
-		actual="$(modebits .git/info/refs)" &&
+		actual="$(test_modebits .git/info/refs)" &&
 		verbose test "x$actual" = "x-$x"
 
 	'
@@ -111,7 +107,7 @@ test_expect_success POSIXPERM 'info/refs respects umask in unshared repo' '
 	umask 002 &&
 	git update-server-info &&
 	echo "-rw-rw-r--" >expect &&
-	modebits .git/info/refs >actual &&
+	test_modebits .git/info/refs >actual &&
 	test_cmp expect actual
 '
 
@@ -177,7 +173,7 @@ test_expect_success POSIXPERM 'remote init does not use config from cwd' '
 	umask 0022 &&
 	git init --bare child.git &&
 	echo "-rw-r--r--" >expect &&
-	modebits child.git/config >actual &&
+	test_modebits child.git/config >actual &&
 	test_cmp expect actual
 '
 
@@ -187,7 +183,7 @@ test_expect_success POSIXPERM 're-init respects core.sharedrepository (local)' '
 	echo whatever >templates/foo &&
 	git init --template=templates &&
 	echo "-rw-rw-rw-" >expect &&
-	modebits .git/foo >actual &&
+	test_modebits .git/foo >actual &&
 	test_cmp expect actual
 '
 
@@ -198,7 +194,7 @@ test_expect_success POSIXPERM 're-init respects core.sharedrepository (remote)'
 	test_path_is_missing child.git/foo &&
 	git init --bare --template=../templates child.git &&
 	echo "-rw-rw-rw-" >expect &&
-	modebits child.git/foo >actual &&
+	test_modebits child.git/foo >actual &&
 	test_cmp expect actual
 '
 
@@ -209,7 +205,7 @@ test_expect_success POSIXPERM 'template can set core.sharedrepository' '
 	cp .git/config templates/config &&
 	git init --bare --template=../templates child.git &&
 	echo "-rw-rw-rw-" >expect &&
-	modebits child.git/HEAD >actual &&
+	test_modebits child.git/HEAD >actual &&
 	test_cmp expect actual
 '
 
diff --git a/t/t1700-split-index.sh b/t/t1700-split-index.sh
index af3ec0da5a..22f69a410b 100755
--- a/t/t1700-split-index.sh
+++ b/t/t1700-split-index.sh
@@ -370,4 +370,34 @@ test_expect_success 'check splitIndex.sharedIndexExpire set to "never" and "now"
 	test $(ls .git/sharedindex.* | wc -l) -le 2
 '
 
+while read -r mode modebits
+do
+	test_expect_success POSIXPERM "split index respects core.sharedrepository $mode" '
+		# Remove existing shared index files
+		git config core.splitIndex false &&
+		git update-index --force-remove one &&
+		rm -f .git/sharedindex.* &&
+		# Create one new shared index file
+		git config core.sharedrepository "$mode" &&
+		git config core.splitIndex true &&
+		: >one &&
+		git update-index --add one &&
+		echo "$modebits" >expect &&
+		test_modebits .git/index >actual &&
+		test_cmp expect actual &&
+		shared=$(ls .git/sharedindex.*) &&
+		case "$shared" in
+		*" "*)
+			# we have more than one???
+			false ;;
+		*)
+			test_modebits "$shared" >actual &&
+			test_cmp expect actual ;;
+		esac
+	'
+done <<\EOF
+0666 -rw-rw-rw-
+0642 -rw-r---w-
+EOF
+
 test_done
diff --git a/t/test-lib-functions.sh b/t/test-lib-functions.sh
index 5ee124332a..db622c3555 100644
--- a/t/test-lib-functions.sh
+++ b/t/test-lib-functions.sh
@@ -216,6 +216,11 @@ test_chmod () {
 	git update-index --add "--chmod=$@"
 }
 
+# Get the modebits from a file.
+test_modebits () {
+	ls -l "$1" | sed -e 's|^\(..........\).*|\1|'
+}
+
 # Unset a configuration variable, but don't fail if it doesn't exist.
 test_unconfig () {
 	config_dir=