diff --git a/docs/topics/extensions.rst b/docs/topics/extensions.rst
index 806a5d63a..f18af83f2 100644
--- a/docs/topics/extensions.rst
+++ b/docs/topics/extensions.rst
@@ -242,6 +242,8 @@ Memory usage extension
 
 .. class:: scrapy.contrib.memusage.MemoryUsage
 
+.. note:: This extension does not work in Windows.
+
 Allows monitoring the memory used by a Scrapy process and:
 
 1, send a notification email when it exceeds a certain value