diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 3f28e20..c25ce11 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -60,6 +60,11 @@ jobs:
           GH_TOKEN: ${{ github.token }}
         run: |
           VERSION=$(ruby -r ./lib/gocardless_pro/version.rb -e 'puts GoCardlessPro::VERSION')
+          # Guard against a crafted version string reaching later shell commands.
+          if [[ ! "$VERSION" =~ ^[0-9]+\.[0-9]+\.[0-9]+([-+][0-9A-Za-z.-]+)?$ ]]; then
+            echo "Refusing to release: '$VERSION' is not a valid semantic version"
+            exit 1
+          fi
           echo "version=$VERSION" >> $GITHUB_OUTPUT
           if gh release view "v$VERSION" >/dev/null 2>&1; then
             echo "already_published=true" >> $GITHUB_OUTPUT
@@ -80,8 +85,9 @@ jobs:
       - name: Extract changelog notes for this version
         id: notes
         if: steps.version_check.outputs.already_published == 'false'
+        env:
+          VERSION: ${{ steps.version_check.outputs.version }}
         run: |
-          VERSION="${{ steps.version_check.outputs.version }}"
           NOTES=""
           if [ -f CHANGELOG.md ]; then
             NOTES=$(awk -v ver="$VERSION" '
@@ -100,9 +106,10 @@ jobs:
         if: steps.version_check.outputs.already_published == 'false'
         env:
           GH_TOKEN: ${{ github.token }}
+          VERSION: ${{ steps.version_check.outputs.version }}
+          NOTES: ${{ steps.notes.outputs.notes }}
         run: |
-          NOTES="${{ steps.notes.outputs.notes }}"
-          TAG="v${{ steps.version_check.outputs.version }}"
+          TAG="v${VERSION}"
           if [ -n "$(echo "$NOTES" | tr -d '[:space:]')" ]; then
             gh release create "$TAG" --title "$TAG" --notes "$NOTES"
           else