diff --git a/.github/workflows/llgo-binary-size-pages.yml b/.github/workflows/llgo-binary-size-pages.yml
index 130dc2b..f634198 100644
--- a/.github/workflows/llgo-binary-size-pages.yml
+++ b/.github/workflows/llgo-binary-size-pages.yml
@@ -39,11 +39,28 @@ jobs:
           GH_TOKEN: ${{ github.token }}
         run: |
           set -euo pipefail
+          set -a
+          source ci/llgo-size/llgo-version.env
+          set +a
+
+          # Rebuild every stored run's main position from the complete LLGo
+          # first-parent history. Result jobs may have been created from old or
+          # shallow checkouts, so their embedded index is only a hint.
+          git clone --filter=blob:none --no-checkout --single-branch --branch main \
+            "https://github.com/${LLGO_REPOSITORY}.git" \
+            "$GITHUB_WORKSPACE/.ci/llgo-history"
+          git -C "$GITHUB_WORKSPACE/.ci/llgo-history" \
+            rev-list --first-parent --reverse origin/main \
+            > "$GITHUB_WORKSPACE/.ci/llgo-main-history.txt"
+
           pages_dir="$GITHUB_WORKSPACE/.ci/pages"
           bash ci/llgo-size/prepare-pages-branch.sh \
             "$pages_dir" \
             "https://x-access-token:${PAGES_TOKEN}@github.com/${GITHUB_REPOSITORY}.git"
-          ci/llgo-size/publish-site.sh "$pages_dir" ci/llgo-size/site
+          ci/llgo-size/publish-site.sh \
+            "$pages_dir" \
+            ci/llgo-size/site \
+            "$GITHUB_WORKSPACE/.ci/llgo-main-history.txt"
 
   deploy-pages:
     if: github.event_name != 'pull_request' && github.ref == 'refs/heads/main'
diff --git a/.github/workflows/llgo-binary-size.yml b/.github/workflows/llgo-binary-size.yml
index 821acc8..635f7db 100644
--- a/.github/workflows/llgo-binary-size.yml
+++ b/.github/workflows/llgo-binary-size.yml
@@ -281,7 +281,10 @@ jobs:
             git -C .ci/llgo fetch --progress --no-tags --depth=1 origin "$LLGO_COMMIT"
           time_command "Check out pinned LLGo commit" \
             git -C .ci/llgo checkout --detach "$LLGO_COMMIT"
-          git -C .ci/llgo fetch --no-tags origin main
+          # The commit-specific depth-1 fetch above makes this repository
+          # shallow. Unshallow it before assigning first-parent positions;
+          # otherwise every run appears to be main index 1.
+          git -C .ci/llgo fetch --no-tags --unshallow origin main
           git -C .ci/llgo rev-list --first-parent --reverse origin/main > .ci/llgo-main-history.txt
           llgo_main_index="$(awk -v commit="$LLGO_COMMIT" '$0 == commit { print NR; exit }' \
             .ci/llgo-main-history.txt)"
diff --git a/ci/llgo-size/publish-site.sh b/ci/llgo-size/publish-site.sh
index 56b15a9..f12dc82 100755
--- a/ci/llgo-size/publish-site.sh
+++ b/ci/llgo-size/publish-site.sh
@@ -4,8 +4,9 @@ set -euo pipefail
 script_dir="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)"
 pages_dir="$1"
 site_dir="$2"
+main_history="${3:-}"
 if [[ -z "$pages_dir" || -z "$site_dir" ]]; then
-  echo "usage: publish-site.sh PAGES_DIR SITE_DIR" >&2
+  echo "usage: publish-site.sh PAGES_DIR SITE_DIR [LLGO_MAIN_HISTORY]" >&2
   exit 2
 fi
 
@@ -14,7 +15,11 @@ for file in index.html app.js performance.html performance.js compatibility.html
 done
 rm -f "$pages_dir/.nojekyll"
 if [[ -s "$pages_dir/data/index.json" ]]; then
-  python3 "$script_dir/enrich_pull_requests.py" "$pages_dir/data/index.json"
+  enrich_args=("$pages_dir/data/index.json")
+  if [[ -n "$main_history" && -s "$main_history" ]]; then
+    enrich_args+=(--main-history "$main_history")
+  fi
+  python3 "$script_dir/enrich_pull_requests.py" "${enrich_args[@]}"
 fi
 
 git -C "$pages_dir" config user.name "github-actions[bot]"
diff --git a/ci/llgo-size/test_enrich_pull_requests.py b/ci/llgo-size/test_enrich_pull_requests.py
index d92be80..e67b218 100644
--- a/ci/llgo-size/test_enrich_pull_requests.py
+++ b/ci/llgo-size/test_enrich_pull_requests.py
@@ -87,11 +87,13 @@ def test_orders_runs_by_llgo_main_history_instead_of_build_completion(self):
                 {
                     "key": second,
                     "llgoCommit": second,
+                    "llgoMainIndex": 1,
                     "createdAt": "2026-08-21T01:00:00Z",
                 },
                 {
                     "key": first,
                     "llgoCommit": first,
+                    "llgoMainIndex": 1,
                     "createdAt": "2026-08-21T02:00:00Z",
                 },
             ]