diff --git a/Doc/library/subprocess.rst b/Doc/library/subprocess.rst
index e09994ce7d5..4c0edb3ebb4 100644
--- a/Doc/library/subprocess.rst
+++ b/Doc/library/subprocess.rst
@@ -217,8 +217,8 @@ This module defines one class called :class:`Popen`:
    *creationflags*, if given, can be :data:`CREATE_NEW_CONSOLE` or
    :data:`CREATE_NEW_PROCESS_GROUP`. (Windows only)
 
-   Popen objects are supported as context managers via the :keyword:`with` statement,
-   closing any open file descriptors on exit.
+   Popen objects are supported as context managers via the :keyword:`with` statement:
+   on exit, standard file descriptors are closed, and the process is waited for.
    ::
 
       with Popen(["ifconfig"], stdout=PIPE) as proc:
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 9856e6a3330..a5381da4407 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -764,6 +764,8 @@ class Popen(object):
             self.stderr.close()
         if self.stdin:
             self.stdin.close()
+        # Wait for the process to terminate, to avoid zombies.
+        self.wait()
 
     def __del__(self, _maxsize=sys.maxsize, _active=_active):
         if not self._child_created:
diff --git a/Lib/test/test_subprocess.py b/Lib/test/test_subprocess.py
index 4ec754c8aae..176ff108e6f 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -1491,7 +1491,8 @@ class ContextManagerTests(ProcessTestCase):
     def test_returncode(self):
         with subprocess.Popen([sys.executable, "-c",
                                "import sys; sys.exit(100)"]) as proc:
-            proc.wait()
+            pass
+        # __exit__ calls wait(), so the returncode should be set
         self.assertEqual(proc.returncode, 100)
 
     def test_communicate_stdin(self):
diff --git a/Misc/NEWS b/Misc/NEWS
index b8b65d249db..de0ce38511e 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,10 @@ What's New in Python 3.2.1?
 Core and Builtins
 -----------------
 
+- Issue #12044: Fixed subprocess.Popen when used as a context manager to
+  wait for the process to end when exiting the context to avoid unintentionally
+  leaving zombie processes around.
+
 - Issue #1195: Fix input() if it is interrupted by CTRL+d and then CTRL+c,
   clear the end-of-file indicator after CTRL+d.