diff --git a/python/sglang/lang/backend/runtime_endpoint.py b/python/sglang/lang/backend/runtime_endpoint.py
index 1573ca68da77..9734d7cbaf12 100644
--- a/python/sglang/lang/backend/runtime_endpoint.py
+++ b/python/sglang/lang/backend/runtime_endpoint.py
@@ -281,13 +281,17 @@ def select(
 
         # Remove extra token if no token healing occurred
         for i in range(len(input_token_logprobs)):
+            # Skip if no logprobs available (can happen on some backends)
+            if not input_token_logprobs[i] or not input_token_logprobs[i][0]:
+                continue
             healed_token_str = input_token_logprobs[i][0][-1]
             if s.text_.endswith(healed_token_str):
                 healed_token_logprob = input_token_logprobs[i][0][0]
-                normalized_prompt_logprobs[i] = (
-                    normalized_prompt_logprobs[i] * len(input_token_logprobs[i])
-                    - healed_token_logprob
-                ) / (len(input_token_logprobs[i]) - 1)
+                num_tokens = len(input_token_logprobs[i])
+                if num_tokens > 1:
+                    normalized_prompt_logprobs[i] = (
+                        normalized_prompt_logprobs[i] * num_tokens - healed_token_logprob
+                    ) / (num_tokens - 1)
                 input_token_logprobs[i] = input_token_logprobs[i][1:]
 
         # Compute unconditional logprobs if required
@@ -349,6 +353,9 @@ def _assert_success(self, res):
 
 def compute_normalized_prompt_logprobs(input_logprobs):
     values = [x[0] for x in input_logprobs if x[0]]
+    if not values:
+        # Return negative infinity if no valid logprobs - this choice should not be selected
+        return float("-inf")
     return sum(values) / len(values)