diff --git a/src/vs/platform/theme/common/tokenClassificationRegistry.ts b/src/vs/platform/theme/common/tokenClassificationRegistry.ts
index 754c93d5bd72a6ef270ba18cc2031ea1ee24bb00..f2fd8eb42643fba1ebcec22da563013c1bf1881a 100644
--- a/src/vs/platform/theme/common/tokenClassificationRegistry.ts
+++ b/src/vs/platform/theme/common/tokenClassificationRegistry.ts
@@ -162,7 +162,7 @@ export namespace SemanticTokenRule {
 			&& TokenStyle.equals(r1.style, r2.style);
 	}
 	export function is(r: any): r is SemanticTokenRule {
-		return r && r.selector && typeof r.selector.selectorString === 'string' && TokenStyle.is(r.style);
+		return r && r.selector && typeof r.selector.id === 'string' && TokenStyle.is(r.style);
 	}
 }