diff --git a/python/sglang/srt/observability/scheduler_metrics_mixin.py b/python/sglang/srt/observability/scheduler_metrics_mixin.py
index 18ea325ba..593d6dd58 100644
--- a/python/sglang/srt/observability/scheduler_metrics_mixin.py
+++ b/python/sglang/srt/observability/scheduler_metrics_mixin.py
@@ -97,7 +97,6 @@ class SchedulerMetricsMixin:
         self.num_generated_tokens = 0
         self.last_decode_stats_tic = time.perf_counter()
         self.last_prefill_stats_tic = time.perf_counter()
-        self.last_prefill_tokens = 0
         self.last_gen_throughput: float = 0.0
         self.last_input_throughput: float = 0.0
         self.step_time_dict = defaultdict(list)  # Dict[batch size -> step time]
@@ -337,10 +336,12 @@ class SchedulerMetricsMixin:
         ):
             return
 
-        gap_latency = time.perf_counter() - self.last_prefill_stats_tic
-        self.last_prefill_stats_tic = time.perf_counter()
-        self.last_input_throughput = self.last_prefill_tokens / gap_latency
-        self.last_prefill_tokens = prefill_stats.log_input_tokens
+        now = time.perf_counter()
+        gap_latency = now - self.last_prefill_stats_tic
+        self.last_prefill_stats_tic = now
+        self.last_input_throughput = (
+            prefill_stats.log_input_tokens / gap_latency if gap_latency > 0 else 0.0
+        )
 
         pool_stats = self.get_pool_stats()
         token_usage_msg = ", ".join(pool_stats.get_prefill_usage_msg_parts()) + ", "