diff --git a/tests/base.py b/tests/base.py
index 7a39e20..5f6022a 100755
--- a/tests/base.py
+++ b/tests/base.py
@@ -38,6 +38,7 @@
 import sys
 import tempfile
 import threading
+import traceback
 import time
 import uuid
 
@@ -1654,13 +1655,18 @@
         self.gearman_server.shutdown()
         self.fake_nodepool.stop()
         self.zk.disconnect()
+        self.printHistory()
         # we whitelist watchdog threads as they have relatively long delays
         # before noticing they should exit, but they should exit on their own.
         threads = [t for t in threading.enumerate()
                    if t.name != 'executor-watchdog']
         if len(threads) > 1:
-            self.log.error("More than one thread is running: %s" % threads)
-        self.printHistory()
+            log_str = ""
+            for thread_id, stack_frame in sys._current_frames().items():
+                log_str += "Thread: %s\n" % thread_id
+                log_str += "".join(traceback.format_stack(stack_frame))
+            self.log.debug(log_str)
+            raise Exception("More than one thread is running: %s" % threads)
 
     def assertCleanShutdown(self):
         pass