diff --git a/more_executors/_impl/retry.py b/more_executors/_impl/retry.py
index 6a955934..04bc7fb1 100644
--- a/more_executors/_impl/retry.py
+++ b/more_executors/_impl/retry.py
@@ -89,7 +89,7 @@ def should_retry(self, attempt, future):
         return False
 
     def sleep_time(self, attempt, future):
-        return min(self._sleep * (self._exponent**(attempt-1)), self._max_sleep)
+        return min(self._sleep * (self._exponent ** (attempt - 1)), self._max_sleep)
 
 
 class RetryJob(object):