diff --git a/bazel/labgrid/strategy/ssh.py b/bazel/labgrid/strategy/ssh.py
index 5a7109b4daf6f5bced6eb6fa539dd41ecf27540f..6781363024cd959b591387f8e3cadd389e8792ed 100644
--- a/bazel/labgrid/strategy/ssh.py
+++ b/bazel/labgrid/strategy/ssh.py
@@ -22,7 +22,7 @@ class SSHStrategy(Strategy):
 
     status = attr.ib(default=Status.unknown)
 
-    network_port = attr.ib(default=None, validator=attr.validators.instance_of(str))
+    network_port = attr.ib(default="", validator=attr.validators.instance_of(str))
 
     def __attrs_post_init__(self):
         super().__attrs_post_init__()