diff --git a/.github/workflows/check-version-bump.yaml b/.github/workflows/check-version-bump.yaml
index 3db4af42..016e7c8a 100644
--- a/.github/workflows/check-version-bump.yaml
+++ b/.github/workflows/check-version-bump.yaml
@@ -22,11 +22,12 @@ jobs:
         run: |
           BASE_SHA="${{ github.event.pull_request.base.sha }}"
           HEAD_SHA="${{ github.event.pull_request.head.sha }}"
+          MERGE_BASE=$(git merge-base "$BASE_SHA" "$HEAD_SHA")
 
-          CHANGED_FILES=$(git diff --name-only "$BASE_SHA" "$HEAD_SHA")
+          CHANGED_FILES=$(git diff --name-only "$MERGE_BASE" "$HEAD_SHA")
 
           if echo "$CHANGED_FILES" | grep -qE "^src/.*\.(py|pyi|proto)$"; then
-            BASE_VERSION=$(git show "$BASE_SHA:pyproject.toml" | grep "^version = " | cut -d'"' -f2)
+            BASE_VERSION=$(git show "$MERGE_BASE:pyproject.toml" | grep "^version = " | cut -d'"' -f2)
             HEAD_VERSION=$(git show "$HEAD_SHA:pyproject.toml" | grep "^version = " | cut -d'"' -f2)
 
             if [ "$BASE_VERSION" = "$HEAD_VERSION" ]; then