diff --git a/action.yml b/action.yml
index 3bba17a..b48984a 100644
--- a/action.yml
+++ b/action.yml
@@ -34,6 +34,7 @@ runs:
       run: |
         : parse toolchain version
         if [[ -z $toolchain ]]; then
+          # GitHub does not enforce `required: true` inputs itself. https://github.com/actions/runner/issues/1070
           echo "'toolchain' is a required input" >&2
           exit 1
         elif [[ $toolchain =~ ^stable' '[0-9]+' '(year|month|week|day)s?' 'ago$ ]]; then
diff --git a/scripts/update-revs.sh b/scripts/update-revs.sh
index 697d135..1d5006e 100755
--- a/scripts/update-revs.sh
+++ b/scripts/update-revs.sh
@@ -33,7 +33,7 @@ for rev in `releases` stable beta nightly; do
     if [[ $rev == 1* ]]; then
         sed -i "/^  toolchain:/,+2d; s/\${{inputs\.toolchain}}/$rev/" action.yml
     else
-        sed -i "s/required: true/required: false\n    default: $rev/" action.yml
+        sed -i "s/^    required: true$/    required: false\n    default: $rev/" action.yml
     fi
     git add action.yml
     git commit --quiet --message "toolchain: $rev"