diff --git a/README.md b/README.md
index edb609c..f4c9dc1 100644
--- a/README.md
+++ b/README.md
@@ -157,7 +157,7 @@ Examples of libraries for performing the above steps include the [Python idna](h
 
 Encodes an IPv4 address according to the conventional [dot-decimal notation](https://en.wikipedia.org/wiki/Dot-decimal_notation) first specificed in [RFC 3986 section 3.2.2 page 20 § 2](https://tools.ietf.org/html/rfc3986#page-20).
 
-Protocols using this codec may encode it as binary value of exactly 4 bytes without
+Protocols using this codec must encode it as binary value of exactly 4 bytes without
 an extra length value.
 
  * String → Binary:
@@ -189,7 +189,7 @@ to string address transformation.
 
 Encodes an IPv6 address according to the rules of [RFC 4291 section 2.2](https://tools.ietf.org/html/rfc4291#section-2.2) and [RFC 5962 section 4](https://tools.ietf.org/html/rfc5952#section-4).
 
-Protocols using this codec may encode it as binary value of exactly 16 bytes without
+Protocols using this codec must encode it as binary value of exactly 16 bytes without
 an extra length value.
 
  * String → Binary:  
@@ -209,7 +209,7 @@ may be a viable alternative for some environments.
 
 Encodes a [TOR rendezvous version 2 service pointer](https://gitweb.torproject.org/torspec.git/tree/rend-spec-v2.txt?id=471af27b55ff3894551109b45848f2ce1002441b#n525) (aka .onion-address) and exposed service port on that system.
 
-Protocols using this codec may encode it as binary value of exactly 12 bytes without
+Protocols using this codec must encode it as binary value of exactly 12 bytes without
 an extra length value.
 
  * String → Binary:
@@ -242,7 +242,7 @@ TBD: Is this really always a base58btc encoded string of at least 5 characters i
 Encodes an unsigned 16-bit integer value (such as a port number) in network byte
 order (big endian).
 
-Protocols using this codec may encode it as binary value of exactly 2 bytes without
+Protocols using this codec must encode it as binary value of exactly 2 bytes without
 an extra length value.
 
  * String → Binary: