diff --git a/src/mred/mredmsw.cxx b/src/mred/mredmsw.cxx
index 35b76b7c7c..bc100a3ced 100644
--- a/src/mred/mredmsw.cxx
+++ b/src/mred/mredmsw.cxx
@@ -931,6 +931,8 @@ void MrEdMSWSleep(float secs, void *fds)
       if (rps[result])
         ReleaseSemaphore(handles[result], 1, NULL);
     }
+
+    scheme_collapse_win_fd(fds); /* cleans up */
   } else if (wxTheApp->keep_going) {
     MsgWaitForMultipleObjects(0, NULL, FALSE,
 			      secs ? msecs : INFINITE,