diff --git a/README.txt b/README.txt
index a218b355..298d6c5e 100644
--- a/README.txt
+++ b/README.txt
@@ -1,5 +1,5 @@
 OpenSlide Python requires:
 
 * Python 2 >= 2.6
-* OpenSlide >= 3.2.0
+* OpenSlide >= 3.3.0
 * Python Imaging Library