diff --git a/x-pack/docs/build.gradle b/x-pack/docs/build.gradle
index 1227549c74a66..2183e5659ebfa 100644
--- a/x-pack/docs/build.gradle
+++ b/x-pack/docs/build.gradle
@@ -38,7 +38,7 @@ tasks.named("yamlRestTest").configure {
   if (BuildParams.isSnapshotBuild()) {
     systemProperty 'tests.rest.blacklist', '*/get-builtin-privileges/*'
   } else {
-    systemProperty 'tests.rest.blacklist', ['*/create-cross-cluster-api-key/*', '*/update-cross-cluster-api-key/*']
+    systemProperty 'tests.rest.blacklist', ['*/create-cross-cluster-api-key/*', '*/update-cross-cluster-api-key/*'].join(',')
   }
 }