diff --git a/.github/workflows/noir.yml b/.github/workflows/noir.yml
index 99b762cf98..fbd96b65ab 100644
--- a/.github/workflows/noir.yml
+++ b/.github/workflows/noir.yml
@@ -26,6 +26,9 @@ jobs:
           nix_path: nixpkgs=channel:nixos-22.11
           github_access_token: ${{ secrets.GITHUB_TOKEN }}
 
+      # The GITHUB_SHA doesn't match the last commit on the PR but is instead a merge commit of the PR into master.
+      # As per GitHub docs:
+      #   Note that GITHUB_SHA for this event is the last merge commit of the pull request merge branch.
       - name: Update barretenberg commit in flake.lock
         run: |
           nix flake lock --override-input barretenberg github:AztecProtocol/barretenberg/${{ env.GITHUB_SHA }}