diff --git a/lefthook.yml b/lefthook.yml
index 28178432c31..40875073fdd 100644
--- a/lefthook.yml
+++ b/lefthook.yml
@@ -15,4 +15,6 @@ post-merge:
 post-checkout:
   commands:
     update-submodules:
-      run: git submodule update --init --recursive
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+      # cf https://git-scm.com/docs/githooks#_post_checkout:
+      # The 3rd argument is 1 for branch checkouts and 0 for file checkouts.
+      run: if test {3} -eq "1"; then git submodule update --init --recursive; fi
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