diff --git a/DEVELOPMENT.txt b/DEVELOPMENT.txt
index 8726394b..daffe705 100644
--- a/DEVELOPMENT.txt
+++ b/DEVELOPMENT.txt
@@ -81,6 +81,9 @@ Stylistic Guidelines
 
      hough(canny(my_image))
 
+ * Use `Py_ssize_t` as data type for all indexing, shape and size variables in
+   C/C++ and Cython code.
+
 Test coverage
 -------------