diff --git a/tools/cloud-build/provision/pr-tests.tf b/tools/cloud-build/provision/pr-tests.tf
index b14906b6d2..becff00909 100644
--- a/tools/cloud-build/provision/pr-tests.tf
+++ b/tools/cloud-build/provision/pr-tests.tf
@@ -37,4 +37,8 @@ resource "google_cloudbuild_trigger" "pr_test" {
     }
   }
 
+  substitutions = {
+    _TEST_PREFIX = "pr-"
+  }
+
 }