diff --git a/.docker/tester.yml b/.docker/tester.yml
index be57831a0c8a8b1d10aca196ac46eaa142392f25..b01219883d60a2586e5ff8f80311287bf6c853a6 100644
--- a/.docker/tester.yml
+++ b/.docker/tester.yml
@@ -5,7 +5,7 @@ services:
     networks:
       - docker_caosnet
     environment:
-      - ENV_CPPLIB_VERSION: $CPPLIB_VERSION
+      - ENV_CPPLIB_VERSION: "$CPPLIB_VERSION"
     volumes:
       - type: bind
         source: ./cert