diff --git a/weboob/browser/browsers.py b/weboob/browser/browsers.py
index 6d5469a4a97f55bc5005c6c62aa27395b43a464c..c143a1679ea47d62081d76f770c1680d87b8da2a 100644
--- a/weboob/browser/browsers.py
+++ b/weboob/browser/browsers.py
@@ -1123,7 +1123,7 @@ def code_verifier(self, bytes_number=64):
         return base64.urlsafe_b64encode(os.urandom(bytes_number)).rstrip(b'=').decode('ascii')
 
     def code_challenge(self, verifier):
-        digest = sha256(verifier).digest()
+        digest = sha256(verifier.encode('utf8')).digest()
         return base64.urlsafe_b64encode(digest).rstrip(b'=').decode('ascii')
 
     def build_authorization_parameters(self):