diff --git a/lib/licenses.nix b/lib/licenses.nix
index c38379ed405b..5dcf1a781f4f 100644
--- a/lib/licenses.nix
+++ b/lib/licenses.nix
@@ -747,6 +747,11 @@ lib.mapAttrs mkLicense (
       fullName = "Historical Permission Notice and Disclaimer - University of California variant";
     };
 
+    hyphenBulgarian = {
+      fullName = "hyphen-bulgarian License";
+      spdxId = "hyphen-bulgarian";
+    };
+
     # Intel's license, seems free
     iasl = {
       spdxId = "Intel-ACPI";
diff --git a/pkgs/by-name/xk/xkeyboard-config/package.nix b/pkgs/by-name/xk/xkeyboard-config/package.nix
index 666de77d7b00..76f05d89a425 100644
--- a/pkgs/by-name/xk/xkeyboard-config/package.nix
+++ b/pkgs/by-name/xk/xkeyboard-config/package.nix
@@ -81,9 +81,7 @@ stdenv.mkDerivation (finalAttrs: {
       mit
       hpnd
       cronyx
-      # there is another unknown license at the end but it seems free
-      # also see this issue https://gitlab.freedesktop.org/xkeyboard-config/xkeyboard-config/-/issues/527
-      free
+      hyphenBulgarian
     ];
     maintainers = [ ];
     platforms = lib.platforms.unix;