--- a/gemato/util.py	
+++ a/gemato/util.py	
@@ -3,6 +3,7 @@ 
 # (c) 2017-2018 Michał Górny
 # Licensed under the terms of 2-clause BSD license
 
+import gc
 import multiprocessing
 import sys
 
@@ -19,6 +20,7 @@ class MultiprocessingPoolWrapper(object):
         self.pool = multiprocessing.Pool(processes=processes)
 
     def __enter__(self):
+        gc.disable()
         return self
 
     def __exit__(self, exc_type, exc_value, exc_cb):
@@ -26,6 +28,7 @@ class MultiprocessingPoolWrapper(object):
             self.pool.close()
             self.pool.join()
         self.pool.terminate()
+        gc.enable()
 
     def map(self, *args, **kwargs):
         return self.pool.map(*args, **kwargs)