diff --git a/Jenkinsfile b/Jenkinsfile
index cc31308..e6410ee 100644
--- a/Jenkinsfile
+++ b/Jenkinsfile
@@ -107,7 +107,7 @@ spec:
                 SEMVER="${BASE}-${BUILD_NUMBER}"
               fi
               # Accept bare semver or leading v (with optional prerelease).
-              if ! echo "$SEMVER" | grep -Eq '^v?[0-9]+\\.[0-9]+\\.[0-9]+(?:[-.][0-9A-Za-z]+)?$'; then
+              if ! echo "$SEMVER" | grep -Eq '^v?[0-9]+\\.[0-9]+\\.[0-9]+([-.][0-9A-Za-z]+)?$'; then
                 SEMVER="0.1.0-${BUILD_NUMBER}"
               fi
               echo "SEMVER=${SEMVER}" > build.env