diff --git a/.github/workflows/foundry.yml b/.github/workflows/foundry.yml
index bacf5e23..969de9be 100644
--- a/.github/workflows/foundry.yml
+++ b/.github/workflows/foundry.yml
@@ -28,6 +28,9 @@ jobs:
       - name: Build contracts & check sizes
         run: forge build --force --sizes # don't use compilation cache
 
+      - name: Check foundry.lock matches submodule pins
+        run: forge build --locked
+
   test:
     needs: build