diff --git a/get-modified-packages/action.yaml b/get-modified-packages/action.yaml
index beef4b4b..7d513fc5 100644
--- a/get-modified-packages/action.yaml
+++ b/get-modified-packages/action.yaml
@@ -2,10 +2,10 @@ name: get-modified-packages
 description: ""
 
 inputs:
-  base-branch:
+  base-sha:
     description: ""
     required: false
-    default: ${{ github.base_ref }}
+    default: ${{ github.event.pull_request.base.sha }}
 
 outputs:
   modified-packages:
@@ -23,7 +23,7 @@ runs:
     - name: Get modified packages
       id: get-modified-packages
       run: |
-        echo "modified-packages=$(${GITHUB_ACTION_PATH}/get-modified-packages.sh origin/${{ inputs.base-branch }})" >> $GITHUB_OUTPUT
+        echo "modified-packages=$(${GITHUB_ACTION_PATH}/get-modified-packages.sh ${{ inputs.base-sha }})" >> $GITHUB_OUTPUT
       shell: bash
 
     - name: Show result
diff --git a/get-modified-packages/get-modified-packages.sh b/get-modified-packages/get-modified-packages.sh
index 6b736b69..781fda77 100755
--- a/get-modified-packages/get-modified-packages.sh
+++ b/get-modified-packages/get-modified-packages.sh
@@ -15,12 +15,10 @@ while [ "${1-}" != "" ]; do
     shift
 done
 
-# base_branch is like "origin/main"
-base_branch="${args[0]}"
-echo "base_branch: $base_branch"
+base_sha="${args[0]}"
 
 # Check args
-if [ "$base_branch" = "" ]; then
+if [ "$base_sha" = "" ]; then
     echo -e "\e[31mPlease input a valid base_branch as the 1st argument.\e[m"
     exit 1
 fi
@@ -52,7 +50,7 @@ function find_package_dir() {
 }
 
 # Find modified files from base branch
-modified_files=$(git diff --name-only "$base_branch"...HEAD)
+modified_files=$(git diff --name-only "$base_sha"...HEAD)
 
 # Find modified packages
 modified_package_dirs=()