diff --git a/.github/workflows/build-singbox-docker.yml b/.github/workflows/build-singbox-docker.yml
index 8f9e7e6..b6de8fc 100644
--- a/.github/workflows/build-singbox-docker.yml
+++ b/.github/workflows/build-singbox-docker.yml
@@ -73,7 +73,7 @@ jobs:
           if [[ -z "${{ github.event.inputs.tag }}" ]]; then
             echo "versioned=etnperlong/sing-box:${{ github.ref_name }}" >> $GITHUB_OUTPUT
           else
-            if [[ -z ${{ steps.tag.outputs.tag_postfix }} ]]; then
+            if [[ -z "${{ steps.tag.outputs.tag_postfix }}" ]]; then
               echo "versioned=etnperlong/sing-box:${{ github.event.inputs.tag }}-${{ steps.tag.outputs.tag_postfix }}" >> $GITHUB_OUTPUT
             else
               echo "versioned=etnperlong/sing-box:${{ github.event.inputs.tag }}" >> $GITHUB_OUTPUT