diff --git a/src/overviewer.h b/src/overviewer.h
index c978773..6eac848 100644
--- a/src/overviewer.h
+++ b/src/overviewer.h
@@ -26,7 +26,7 @@
 
 // increment this value if you've made a change to the c extesion
 // and want to force users to rebuild
-#define OVERVIEWER_EXTENSION_VERSION 2
+#define OVERVIEWER_EXTENSION_VERSION 3
 
 /* Python PIL, and numpy headers */
 #include <Python.h>