diff --git a/.trunk/trunk.yaml b/.trunk/trunk.yaml
index 7cdfae6..686c010 100644
--- a/.trunk/trunk.yaml
+++ b/.trunk/trunk.yaml
@@ -13,6 +13,13 @@ repo:
     name: src
 lint:
   definitions:
+    # This repository is consumed as a submodule, so `.git` is a file whose
+    # gitdir is relative to the superproject. Trunk's sandbox copy breaks that
+    # relative path, so anchor the command at the real workspace.
+    - name: git-diff-check
+      commands:
+        - name: lint
+          run: git -C "${workspace}" diff --check ${target}
     - name: shfmt
       commands:
         - name: format