diff --git a/doc/specs/thrift-compact-protocol.md b/doc/specs/thrift-compact-protocol.md
index 6be2a62..001bb12 100644
--- a/doc/specs/thrift-compact-protocol.md
+++ b/doc/specs/thrift-compact-protocol.md
@@ -92,7 +92,8 @@
 
 ### String encoding
 
-*String*s are first encoded to UTF-8, and then send as binary.
+*String*s are first encoded to UTF-8, and then send as binary. They do not
+include a NUL delimiter.
 
 ### Double encoding