diff --git a/respodns/util.py b/respodns/util.py
index af18cae..b1b4787 100644
--- a/respodns/util.py
+++ b/respodns/util.py
@@ -64,7 +64,8 @@ def make_pooler(pool_size, finisher=None):
         desired_size = 0 if finish else pool_size - 1
         while len(pending) > desired_size:
             done, pending = await wait(pending, return_when=FIRST_COMPLETED)
-            finisher(done, pending)
+            if finisher is not None:
+                finisher(done, pending)
 
     return pooler