diff --git a/pep-0437.txt b/pep-0437.txt
index 140740c0c..f80a76fc1 100644
--- a/pep-0437.txt
+++ b/pep-0437.txt
@@ -108,6 +108,10 @@ ampersand.
 Additional declarations may be placed into .c files. Duplicate declarations
 are allowed as long as the function types are identical.
 
+It is encouraged to declare custom converter types a second time right
+above the converter function definition. The preprocessor will then catch
+any mismatch between the declarations.
+
 
 TBD: Make a list of fantasy types like *rw_buffer*.