diff --git a/hfppl/distributions/lmcontext.py b/hfppl/distributions/lmcontext.py
index ba0626a..233892a 100644
--- a/hfppl/distributions/lmcontext.py
+++ b/hfppl/distributions/lmcontext.py
@@ -78,8 +78,13 @@ async def log_prob(self, v):
             if v
             else self.ctx.model_mask - self.mask
         )
+        if len(good_tokens) == 0:
+            # If there are no good tokens, the log probability of v under the mask is -inf
+            logprob_good = float("-inf")
+        else:
+            logprob_good = logsumexp(self.ctx.next_token_logprobs[list(good_tokens)])
+
         bad_tokens = [i for i in self.ctx.model_mask if i not in good_tokens]
-        logprob_good = logsumexp(self.ctx.next_token_logprobs[list(good_tokens)])
         self.ctx.next_token_logprobs[bad_tokens] = float("-inf")
         self.ctx.next_token_logprobs -= logprob_good
         self.ctx.model_mask = good_tokens