diff --git a/scripts/joinmarket-qt.py b/scripts/joinmarket-qt.py
index 29b305831..34badaf47 100644
--- a/scripts/joinmarket-qt.py
+++ b/scripts/joinmarket-qt.py
@@ -1915,7 +1915,7 @@ def onTabChange(i):
     jm_single().bc_interface.simulating = True
     jm_single().maker_timeout_sec = 15
     #trigger start with a fake tx
-    jm_single().bc_interface.pushtx("00"*20)
+    jm_single().bc_interface.pushtx(b"\x00"*20)
 
 #prepare for logging
 for dname in ['logs', 'wallets', 'cmtdata']: