diff --git a/weboob/browser/browsers.py b/weboob/browser/browsers.py
index 15a26b0280e93418488097cd179925f1d6197d3c..d3b8dc27cb708196f7d86f9fb8f4faa2e82ab1d0 100644
--- a/weboob/browser/browsers.py
+++ b/weboob/browser/browsers.py
@@ -1087,11 +1087,11 @@ def __init__(self, *args, **kwargs):
 
     # PKCE (Proof Key for Code Exchange) standard protocol methods:
     def code_verifier(self, bytes_number=64):
-        return base64.urlsafe_b64encode(os.urandom(bytes_number)).rstrip(b'=')
+        return base64.urlsafe_b64encode(os.urandom(bytes_number)).rstrip(b'=').decode('ascii')
 
     def code_challenge(self, verifier):
         digest = sha256(verifier).digest()
-        return base64.urlsafe_b64encode(digest).rstrip(b'=')
+        return base64.urlsafe_b64encode(digest).rstrip(b'=').decode('ascii')
 
     def build_authorization_parameters(self):
         return {'redirect_uri':    self.redirect_uri,