diff --git a/doc/em/app.codes.nr b/doc/em/app.codes.nr
index 8aa2bb6fe..9091f74fe 100644
--- a/doc/em/app.codes.nr
+++ b/doc/em/app.codes.nr
@@ -35,6 +35,8 @@ opcode with 2-byte signed argument
 opcode with 4-byte signed argument
 .PT 8
 opcode with 8-byte signed argument
+.PT u
+opcode with 2-byte unsigned argument
 .PE
 Secondary (escaped) opcodes.
 .PS - 5 "  "