diff --git a/libwccl/values/tset.h b/libwccl/values/tset.h
index 228023d562bcac98a382c2b2fa039e19a13f71e8..a89d0eb27d3449cd1f77f4d450f610800bdb769b 100644
--- a/libwccl/values/tset.h
+++ b/libwccl/values/tset.h
@@ -40,7 +40,7 @@ public:
 	/**
 	 * Alias of get_value()
 	 */
-	Corpus2::Tag& contents() {
+	const Corpus2::Tag& contents() const {
 		return tag_;
 	}