diff --git a/doc/api/crypto.rst b/doc/api/crypto.rst
index 41b659b..27da7e8 100644
--- a/doc/api/crypto.rst
+++ b/doc/api/crypto.rst
@@ -34,11 +34,15 @@
 Serialization and deserialization
 ---------------------------------
 
-The following serialization functions take one of these constants to
-determine the format:
+The following serialization functions take one of these constants to determine the format.
 
 .. py:data:: FILETYPE_PEM
-             FILETYPE_ASN1
+
+:data:`FILETYPE_PEM` serializes data to a Base64-encoded encoded representation of the underlying ASN.1 data structure. This representation includes delimiters that define what data structure is contained within the Base64-encoded block: for example, for a certificate, the delimiters are ``-----BEGIN CERTIFICATE-----`` and ``-----END CERTIFICATE-----``.
+
+.. py:data:: FILETYPE_ASN1
+
+:data:`FILETYPE_ASN1` serializes data to the underlying ASN.1 data structure. The format used by :data:`FILETYPE_ASN1` is also sometimes referred to as DER.
 
 Certificates
 ~~~~~~~~~~~~