diff --git a/lib/licenses/licenses.nix b/lib/licenses/licenses.nix
index 12301021e9c8..63fbee3cd489 100644
--- a/lib/licenses/licenses.nix
+++ b/lib/licenses/licenses.nix
@@ -522,6 +522,11 @@ lib.mapAttrs mkLicense (
       fullName = "DOC License";
     };
 
+    docBookDtd = {
+      spdxId = "DocBook-DTD";
+      fullName = "DocBook DTD License";
+    };
+
     drl10 = {
       spdxId = "DRL-1.0";
       fullName = "Detection Rule License 1.0";