diff --git a/include/boost/python/str.hpp b/include/boost/python/str.hpp
index 758aa79e..dd6548ab 100644
--- a/include/boost/python/str.hpp
+++ b/include/boost/python/str.hpp
@@ -11,6 +11,7 @@
 #undef isalpha
 #undef isdigit
 #undef isalnum
+#undef isupper
 
 namespace boost { namespace python {