diff --git a/vllm/sampling_params.py b/vllm/sampling_params.py
index 5c6df5aaf5446..fc77f3ca529b2 100644
--- a/vllm/sampling_params.py
+++ b/vllm/sampling_params.py
@@ -293,8 +293,9 @@ def __post_init__(self) -> None:
                 raise ValueError(
                     f"best_of must be greater than or equal to n, "
                     f"got n={self.n} and best_of={self.best_of}.")
-            self._real_n = self.n
-            self.n = self.best_of
+            if not self._real_n:
+                self._real_n = self.n
+                self.n = self.best_of
 
         if 0 < self.temperature < _MAX_TEMP:
             logger.warning(