diff --git a/.ci/Jenkinsfile b/.ci/Jenkinsfile
index 356a5c573f..be54d71f2e 100644
--- a/.ci/Jenkinsfile
+++ b/.ci/Jenkinsfile
@@ -320,9 +320,9 @@ def generateFunctionalTestStep(Map args = [:]){
   // On the other hand, the developers can use the TAGS environment variable locally.
   // Finally, we positively know that tags are not empty, so we can use AND operator.
   if ("${NIGHTLY_SCENARIOS}" == "true") {
-    tags + " && ${NIGHTLY_TAG}"
+    tags += " && ${NIGHTLY_TAG}"
   } else {
-    tags + " && ~${NIGHTLY_TAG}"
+    tags += " && ~${NIGHTLY_TAG}"
   }
 
   return {