diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 94d949c21cb88652c0f9c4dc270c480db8f3cb7b..e99feb26d19f1177a9bbc74a2bea428c10005899 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -40,10 +40,10 @@ variables:
   GIT_CLONE_PATH: $CI_BUILDS_DIR/$CI_PROJECT_PATH/$CI_JOB_NAME
   # ↓ reduces the amount of data transfered to the runner (shallow clone)
   GIT_DEPTH: 2
-  DEV: 'https://ahikar-dev.sub.uni-goettingen.de'
+  DEV_URL: 'https://ahikar-dev.sub.uni-goettingen.de'
   MAIN: 'https://ahikar.sub.uni-goettingen.de'
-  API_DEV: ${DEV}/api
-  API_MAIN: ${MAIN}/api
+  API_DEV: "${DEV_URL}/api"
+  API_MAIN: "${MAIN}/api"
   BASE_BACKEND: '/website'
 
 
@@ -68,8 +68,8 @@ install:
 
 build_page-all:
   variables:
-    VUE_APP_BASE_URL_API: ${API_DEV}
-    VUE_APP_BASE_URL_VIEWER: ${DEV}
+    VUE_APP_BASE_URL_API: "${API_DEV}"
+    VUE_APP_BASE_URL_VIEWER: "${DEV_URL}"
     VUE_APP_PUBLIC_PATH: '/ahiqar/website/${CI_COMMIT_REF_SLUG}/'
   <<: *build-defaults
 
@@ -77,18 +77,18 @@ build_page-develop-backend:
   only:
     - develop
   variables:
-    VUE_APP_BASE_URL_API: ${API_DEV}
-    VUE_APP_BASE_URL_VIEWER: ${DEV}
-    VUE_APP_PUBLIC_PATH: ${BASE_BACKEND}
+    VUE_APP_BASE_URL_API: "${API_DEV}"
+    VUE_APP_BASE_URL_VIEWER: "${DEV_URL}"
+    VUE_APP_PUBLIC_PATH: "${BASE_BACKEND}"
   <<: *build-defaults
 
 build_page-main-backend:
   only:
     - main
   variables:
-    VUE_APP_BASE_URL_API: ${API_MAIN}
-    VUE_APP_BASE_URL_VIEWER: ${MAIN}
-    VUE_APP_PUBLIC_PATH: ${BASE_BACKEND}
+    VUE_APP_BASE_URL_API: "${API_MAIN}"
+    VUE_APP_BASE_URL_VIEWER: "${MAIN}"
+    VUE_APP_PUBLIC_PATH: "${BASE_BACKEND}"
   <<: *build-defaults