diff --git a/schema/bom-1.6.proto b/schema/bom-1.6.proto
index 573b4435..78ed6d92 100644
--- a/schema/bom-1.6.proto
+++ b/schema/bom-1.6.proto
@@ -296,6 +296,8 @@ enum ExternalReferenceType {
   EXTERNAL_REFERENCE_TYPE_DIGITAL_SIGNATURE = 40;
   // Document that complies with RFC-9116 (A File Format to Aid in Security Vulnerability Disclosure)
   EXTERNAL_REFERENCE_TYPE_RFC_9116 = 41;
+  // URL to release notes
+  EXTERNAL_REFERENCE_TYPE_RELEASE_NOTES = 42;
 }
 
 enum HashAlg {