diff --git a/runbot/models/build.py b/runbot/models/build.py
index 5f28ee71..c1687495 100644
--- a/runbot/models/build.py
+++ b/runbot/models/build.py
@@ -377,7 +377,7 @@ class runbot_build(models.Model):
 
         # find next free port
         while port in ports:
-            port += 2
+            port += 3
         return port
 
     def _logger(self, *l):