diff --git a/lib/thread.rb b/lib/thread.rb
index 22dba2d..1d1fcb2 100644
--- a/lib/thread.rb
+++ b/lib/thread.rb
@@ -185,7 +185,7 @@ class Queue
       while true
         if @que.empty?
           raise ThreadError, "queue empty" if non_block
-          @waiting.push Thread.current
+          @waiting.push Thread.current unless @waiting.include?(Thread.current)
           @mutex.sleep
         else
           return @que.shift