--- a/cubicweb/toolsutils.py	Thu May 03 16:47:51 2018 +0200
+++ b/cubicweb/toolsutils.py	Wed Jun 06 11:56:15 2018 +0200
@@ -96,7 +96,7 @@
     """
     import shutil
     pipe = subprocess.Popen(['diff', '-u', appl_file, ref_file], stdout=subprocess.PIPE)
-    diffs = pipe.stdout.read()
+    diffs = pipe.stdout.read().decode('utf-8')
     if diffs:
         if askconfirm:
             print()