diff --git a/labscript/base.py b/labscript/base.py
index cbab6b6..e57ab9d 100644
--- a/labscript/base.py
+++ b/labscript/base.py
@@ -93,6 +93,7 @@ def __init__(
         self.connection = connection
         self.start_order = start_order
         self.stop_order = stop_order
+        self.BLACS_connection = ""
         if start_order is not None and not isinstance(start_order, int):
             raise TypeError(
                 f"Error when instantiating {name}. start_order must be an integer, not "
diff --git a/labscript/labscript.py b/labscript/labscript.py
index 6e1d23f..037c59f 100644
--- a/labscript/labscript.py
+++ b/labscript/labscript.py
@@ -229,7 +229,7 @@ def generate_connection_table(hdf5_file):
     devicedict = {}
     
     # Only use a string dtype as long as is needed:
-    max_BLACS_conn_length = -1
+    max_BLACS_conn_length = 0
 
     for device in compiler.inventory:
         devicedict[device.name] = device