diff --git a/test-parser.mjs b/test-parser.mjs
index 1c2aab2..599e694 100644
--- a/test-parser.mjs
+++ b/test-parser.mjs
@@ -666,6 +666,20 @@ ok('adjacent: null when absent', adjOffset.stemNotes[0].adjacent === null);
 ok('adjacent: false when False', adjOffset.stemNotes[1].adjacent === false);
 ok('adjacent: true when True', adjOffset.stemNotes[2].adjacent === true);
 
+section('unknownSlots graceful degradation');
+const UNK_FIXTURE = `00 instrument 'test'
+01 character.FUTURE_SLOT foo='bar'
+01 character.variation
+02 variation.ANOTHER_UNKNOWN x=1
+`;
+const unkModel = buildModel(parseAstLog(UNK_FIXTURE));
+const unkInstr = unkModel.instruments[0];
+ok('unknown slot: instrument parsed', !!unkInstr);
+ok('unknown slot: rawChildren is array', Array.isArray(unkInstr.rawChildren));
+ok('unknown slot: instrument-level unknown collected', unkInstr.rawChildren.length === 1);
+ok('unknown slot: collected slot type', unkInstr.rawChildren[0].type === 'FUTURE_SLOT');
+ok('variation-level unknown collected', unkInstr.variations[0]?.rawChildren?.length === 1);
+
 section('Full fixture integration');
 ok('fixture parses without error (checked above)', raw && raw.slot === 'root');
 ok('fixture has 432 bars', model.bars.length === 432);