diff --git a/tests/test-fix.t b/tests/test-fix.t
--- a/tests/test-fix.t
+++ b/tests/test-fix.t
@@ -3,10 +3,19 @@
 
   $ UPPERCASEPY="$TESTTMP/uppercase.py"
   $ cat > $UPPERCASEPY <<EOF
+  > import io
   > import sys
   > from mercurial.utils.procutil import setbinary
   > setbinary(sys.stdin)
   > setbinary(sys.stdout)
+  > if sys.version_info[0] >= 3:
+  >     sys.stdout = io.TextIOWrapper(
+  >         sys.stdout.buffer,
+  >         sys.stdout.encoding,
+  >         sys.stdout.errors,
+  >         newline="\n",
+  >         line_buffering=sys.stdout.line_buffering,
+  >     )
   > lines = set()
   > for arg in sys.argv[1:]:
   >   if arg == 'all':