merge - 7a3f3ad83676  Fixes Issue #12044.
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
index 9856e6a..a5381da 100644
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -764,6 +764,8 @@
             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 4ec754c..176ff10 100644
--- a/Lib/test/test_subprocess.py
+++ b/Lib/test/test_subprocess.py
@@ -1491,7 +1491,8 @@
     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):