diff --git a/vllm/v1/core/scheduler.py b/vllm/v1/core/scheduler.py
index 614558155e45e..08e7c0fd4dc9b 100644
--- a/vllm/v1/core/scheduler.py
+++ b/vllm/v1/core/scheduler.py
@@ -208,6 +208,7 @@ def schedule(self) -> "SchedulerOutput":
                     num_new_tokens = self.block_size
                     computed_blocks.pop()
                 num_new_tokens = min(num_new_tokens, token_budget)
+                assert num_new_tokens > 0
 
                 # Schedule encoder inputs.
                 (encoder_inputs_to_schedule, num_new_tokens,