diff --git a/tests/flagprocessorext.py b/tests/flagprocessorext.py
--- a/tests/flagprocessorext.py
+++ b/tests/flagprocessorext.py
@@ -107,7 +107,7 @@
 
     # Teach exchange to use changegroup 3
     for k in exchange._bundlespeccontentopts.keys():
-        exchange._bundlespeccontentopts[k]["cg.version"] = "03"
+        exchange._bundlespeccontentopts[k][b"cg.version"] = b"03"
 
     # Register flag processors for each extension
     revlog.addflagprocessor(