1 files changed, 7 insertions, 0 deletions

diff --git a/src/mailman/bin/master.py b/src/mailman/bin/master.py
index 0b273d332..ccaa16398 100644
--- a/src/mailman/bin/master.py
+++ b/src/mailman/bin/master.py
@@ -188,6 +188,9 @@ 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
@@ -402,6 +405,10 @@ class Loop:
             except InterruptedError:                # pragma: nocover
                 # If the system call got interrupted, just restart it.
                 continue
+            if pid not in self._kids:  # pragma: nocover
+                # 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):