1 files changed, 7 insertions, 0 deletions

diff --git a/src/mailman/bin/master.py b/src/mailman/bin/master.py
index c6a8bcd2d..ef64f3d83 100644
--- a/src/mailman/bin/master.py
+++ b/src/mailman/bin/master.py
@@ -230,6 +230,9 @@ class PIDWatcher:
     def __init__(self):
         self._pids = {}
 
+    def __contains__(self, pid):
+        return pid in self._pids.keys()
+
     def __iter__(self):
         # Safely iterate over all the keys in the dictionary.  Because
         # asynchronous signals are involved, the dictionary's size could
@@ -447,6 +450,10 @@ class Loop:
                     continue
                 else:
                     raise
+            if pid not in self._kids:
+                # Not a runner subprocess, maybe a plugin started one
+                # ignore it
+                continue
             # Find out why the subprocess exited by getting the signal
             # received or exit status.
             if os.WIFSIGNALED(status):