diff --git a/.github/workflows/update-submodules.yml b/.github/workflows/update-submodules.yml
index 5c94fc4..2806367 100644
--- a/.github/workflows/update-submodules.yml
+++ b/.github/workflows/update-submodules.yml
@@ -1,7 +1,8 @@
 ---
 name: Update submodules
 on:
-  schedule: [{ cron: 0 3 * * * }]
+  # At 04:00 on Monday and Thursday.
+  schedule: "0 4 * * 1,4"
   workflow_dispatch:
 jobs:
   update-submodules: