diff --git a/setup/management.sh b/setup/management.sh
index 0f6e4d0a..7ea1332b 100755
--- a/setup/management.sh
+++ b/setup/management.sh
@@ -8,7 +8,7 @@ hide_output pip3 install rtyaml
 # Create a backup directory and a random key for encrypting backups.
 mkdir -p $STORAGE_ROOT/backup
 if [ ! -f $STORAGE_ROOT/backup/secret_key.txt ]; then
-	openssl rand -base64 2048 > $STORAGE_ROOT/backup/secret_key.txt
+	$(umask 077; openssl rand -base64 2048 > $STORAGE_ROOT/backup/secret_key.txt)
 fi
 
 # Link the management server daemon into a well known location.
diff --git a/setup/migrate.py b/setup/migrate.py
index 87c915ab..d2ecff24 100755
--- a/setup/migrate.py
+++ b/setup/migrate.py
@@ -56,6 +56,10 @@ def migration_4(env):
 	db = os.path.join(env["STORAGE_ROOT"], 'mail/users.sqlite')
 	shell("check_call", ["sqlite3", db, "ALTER TABLE users ADD privileges TEXT NOT NULL DEFAULT ''"])
 
+def migration_5(env):
+        # The secret key for encrypting backups was world readable. Fix here.
+        os.chmod(os.path.join(env["STORAGE_ROOT"], 'backup/secret_key.txt'), 0o600)
+
 def get_current_migration():
 	ver = 0
 	while True: