diff --git a/gemma/gm/text/_chat_sampler.py b/gemma/gm/text/_chat_sampler.py
index 12f6d04d..bbb24522 100644
--- a/gemma/gm/text/_chat_sampler.py
+++ b/gemma/gm/text/_chat_sampler.py
@@ -272,9 +272,9 @@ def _remove_eos_token(
   return dataclasses.replace(
       state,
       step=state.step - 1,
-      # done is True and last_token is EOS => False
+      # done is True and last_token is EOS => False (un-done it)
       # Otherwise, keep the same.
-      done=state.done ^ (state.last_token == tokenizer.special_tokens.EOS),
+      done=state.done & ~(state.last_token == tokenizer.special_tokens.EOS),
       last_token_pos=state.last_token_pos - 1,
       cache=cache_info.cache,
   )
diff --git a/gemma/gm/text/_sampler.py b/gemma/gm/text/_sampler.py
index 5b8ae163..710e321d 100644
--- a/gemma/gm/text/_sampler.py
+++ b/gemma/gm/text/_sampler.py
@@ -577,7 +577,7 @@ def _normalize_token(tokenizer, token: str | int) -> int:
   token_id = tokenizer.encode(token)
   if len(token_id) != 1:
     raise ValueError(
-        'Invalid token: {token!r}. `stop_token`s and `forbidden_token`s must'
+        f'Invalid token: {token!r}. `stop_token`s and `forbidden_token`s must'
         ' map to single token ids in the vocab.'
     )
   (token_id,) = token_id