diff --git a/src/Test/TestThreadPool.py b/src/Test/TestThreadPool.py
index caf4863a9..2a67f181d 100644
--- a/src/Test/TestThreadPool.py
+++ b/src/Test/TestThreadPool.py
@@ -16,6 +16,8 @@ def blocker():
             events.append("S")
             out = 0
             for i in range(10000000):
+                if i == 5000000:
+                    events.append("M")
                 out += 1
             events.append("D")
             return out
@@ -25,7 +27,7 @@ def blocker():
             threads.append(gevent.spawn(blocker))
         gevent.joinall(threads)
 
-        assert events == ["S"] * 4 + ["D"] * 4
+        assert events == ["S"] * 4 + ["M"] * 4 + ["D"] * 4
 
         res = blocker()
         assert res == 10000000