diff --git a/hgext/transplant.py b/hgext/transplant.py
--- a/hgext/transplant.py
+++ b/hgext/transplant.py
@@ -311,7 +311,7 @@
                 p1 = repo.dirstate.p1()
                 p2 = node
                 self.log(user, date, message, p1, p2, merge=merge)
-                self.ui.write(str(inst) + '\n')
+                self.ui.write(util.forcebytestr(inst) + '\n')
                 raise TransplantError(_('fix up the working directory and run '
                                         'hg transplant --continue'))
         else:
diff --git a/mercurial/patch.py b/mercurial/patch.py
--- a/mercurial/patch.py
+++ b/mercurial/patch.py
@@ -1459,7 +1459,7 @@
                 dec.append(util.b85decode(line[1:])[:l])
             except ValueError as e:
                 raise PatchError(_('could not decode "%s" binary patch: %s')
-                                 % (self._fname, str(e)))
+                                 % (self._fname, util.forcebytestr(e)))
             line = getline(lr, self.hunk)
         text = zlib.decompress(''.join(dec))
         if len(text) != size: