diff --git a/lib/timeout.rb b/lib/timeout.rb
index 91b04a9..cbf6d54 100644
--- a/lib/timeout.rb
+++ b/lib/timeout.rb
@@ -177,6 +177,7 @@ def interrupt
     def finished
       Sync.synchronize @mutex do
         @done = true
+        @thread = nil
       end
     end
   end