diff --git a/benchmarks/ddb.pyon b/benchmarks/ddb.pyon
index 7dce005a0..3842a5e18 100644
--- a/benchmarks/ddb.pyon
+++ b/benchmarks/ddb.pyon
@@ -3,7 +3,7 @@
         "type": "local",
         "module": "artiq.coredevice.comm_serial",
         "class": "Comm",
-        "arguments": {}
+        "arguments": {"serial_dev": "/dev/ttyUSB1"}
     },
     "core": {
         "type": "local",
diff --git a/examples/master/ddb.pyon b/examples/master/ddb.pyon
index 26c419701..b602d367a 100644
--- a/examples/master/ddb.pyon
+++ b/examples/master/ddb.pyon
@@ -3,7 +3,7 @@
         "type": "local",
         "module": "artiq.coredevice.comm_serial",
         "class": "Comm",
-        "arguments": {}
+        "arguments": {"serial_dev": "/dev/ttyUSB1"}
     },
     "core": {
         "type": "local",