diff --git a/ait/core/tlm.py b/ait/core/tlm.py
index <HASH>..<HASH> 100644
--- a/ait/core/tlm.py
+++ b/ait/core/tlm.py
@@ -743,7 +743,7 @@ class PacketDefinition(json.SlotSerializer, object):
 
     def simulate(self, fill=None):
         size   = self.nbytes
-        values = bytearray(range(size)) if fill is None else bytearray(str(fill) * size, 'ascii')
+        values = bytearray(range(size)) if fill is None else bytearray(str(fill) * size, 'utf-8')
         return Packet(self, values)
Updated tlm simulate to use utf-8 encoding