diff --git a/iana_matroska_ids.md b/iana_matroska_ids.md
index fea82e5b..7e33fc73 100644
--- a/iana_matroska_ids.md
+++ b/iana_matroska_ids.md
@@ -21,8 +21,14 @@ One-octet Matroska Element IDs (range 0x80-0xFE) are to be allocated according t
 
 Two-octet Matroska Element IDs (range 0x407F-0x7FFE) are to be allocated according to the "Specification Required" policy [@!RFC8126].
 
+Two-octet Matroska Element IDs between 0x0100 and 0x407E are not valid for use as an Element ID.
+
 Three-octet (range 0x203FFF-0x3FFFFE) and four-octet Matroska Element IDs (range 0x101FFFFF-0x1FFFFFFE) are to be allocated according to the "First Come First Served" policy [@!RFC8126].
 
+Three-octet Matroska Element IDs between 0x010000 and 0x203FFE are not valid for use as an Element ID.
+
+Four-octet Matroska Element IDs between 0x01000000 and 0x101FFFFE are not valid for use as an Element ID.
+
 The allowed values in the "Matroska Element IDs" registry are similar to the ones found
 in the "EBML Element IDs" registry defined in [@!RFC8794, section 17.1].