diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index 92d5272..d95b33c 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -1609,7 +1609,7 @@
       the process pool as separate tasks.  The (approximate) size of these
       chunks can be specified by setting *chunksize* to a positive integer.
 
-   .. method:: map_async(func, iterable[, chunksize[, callback]])
+   .. method:: map_async(func, iterable[, chunksize[, callback[, error_callback]]])
 
       A variant of the :meth:`.map` method which returns a result object.