Index: frontend/src/components/SubjectCatalog/FavoriteButton.tsx
===================================================================
--- frontend/src/components/SubjectCatalog/FavoriteButton.tsx	(revision 77901201e9f51078c422b3061c48926d113882fd)
+++ frontend/src/components/SubjectCatalog/FavoriteButton.tsx	(revision 2dcd2e90570e37b58c5c237905918997562016a4)
@@ -27,4 +27,5 @@
 	const { isAuthenticated } = useAuth();
 	const isFavorite = favoriteIds.has(subjectId);
+	const isFilled = isAuthenticated && isFavorite;
 
 	return (
@@ -37,5 +38,5 @@
 			aria-label={isFavorite ? "Unfavorite" : "Favorite"}
 		>
-			<HeartIcon filled={isFavorite} />
+			<HeartIcon filled={isFilled} />
 		</button>
 	);