diff --git a/.github/workflows/monorepo-release.yml b/.github/workflows/monorepo-release.yml
index 4290e18..615e869 100644
--- a/.github/workflows/monorepo-release.yml
+++ b/.github/workflows/monorepo-release.yml
@@ -39,6 +39,13 @@ jobs:
         run: |
           VERSION=$(grep -m1 '^version' pyproject.toml \
             | sed 's/version *= *"\(.*\)"/\1/')
+
+          # Validate format before writing to GITHUB_OUTPUT
+          if [[ ! "$VERSION" =~ ^[0-9a-zA-Z._-]+$ ]]; then
+            echo "::error::Unexpected version format: '${VERSION}'" >&2
+            exit 1
+          fi
+
           echo "version=${VERSION}" >> "$GITHUB_OUTPUT"
           echo "tag=v${VERSION}" >> "$GITHUB_OUTPUT"
           echo "Monorepo version: ${VERSION}"