Index: twisted/internet/posixbase.py
===================================================================
--- twisted/internet/posixbase.py	(revision 17839)
+++ twisted/internet/posixbase.py	(working copy)
@@ -198,10 +198,7 @@
         eventloop round prevents us from violating the state constraints
         of arbitrary classes.
         """
-        if _threadSupport:
-            self.callFromThread(process.reapAllProcesses)
-        else:
-            self.callLater(0, process.reapAllProcesses)
+        self.callFromThread(process.reapAllProcesses)
 
     def startRunning(self, installSignalHandlers=1):
         # Just in case we're started on a different thread than