diff --git a/roles/run-tempest-26/tasks/main.yaml b/roles/run-tempest-26/tasks/main.yaml
index 7423bfb..7ad5c99 100644
--- a/roles/run-tempest-26/tasks/main.yaml
+++ b/roles/run-tempest-26/tasks/main.yaml
@@ -17,7 +17,7 @@
 
 - name: Limit max concurrency when more than 3 vcpus are available
   set_fact:
-    default_concurrency: "{{ num_cores|int // 2 }}"
+    default_concurrency: "{{ num_cores|int - 2 }}"
   when: num_cores|int > 3
 
 - name: Override target branch