diff --git a/Dockerfile b/Dockerfile
index edc1c3c..d97e542 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -25,7 +25,7 @@ ENV DB_SCHEMA ${DB_SCHEMA:-public}
 ENV KEYCLOAK_USER ${KEYCLOAK_USER:-admin}
 ENV KEYCLOAK_PASSWORD ${SETUP_ADMIN_PASSWORD:-secret}
 ENV PROXY_ADDRESS_FORWARDING ${PROXY_ADDRESS_FORWARDING:-true}
-ENV KEYCLOAK_FRONTEND_URL ${KEYCLOAK_FRONTEND_URL:}
+ENV KEYCLOAK_FRONTEND_URL ${KEYCLOAK_FRONTEND_URL:-}
 ENV TZ ${TZ:-Europe/Amsterdam}
 
 ARG GIT_REPO