diff --git a/src/calibre/gui2/tweak_book/diff/main.py b/src/calibre/gui2/tweak_book/diff/main.py
index 9db5ac7ba2..7280b7fd7b 100644
--- a/src/calibre/gui2/tweak_book/diff/main.py
+++ b/src/calibre/gui2/tweak_book/diff/main.py
@@ -118,7 +118,10 @@ def get_decoded_raw(name):
             try:
                 raw = raw.decode(enc)
             except (LookupError, ValueError):
-                pass
+                try:
+                    raw = raw.decode('utf-8')
+                except ValueError:
+                    pass
     return raw, syntax