diff --git a/ImperatorToCK3/CK3/Titles/Title.cs b/ImperatorToCK3/CK3/Titles/Title.cs
index 9fa1a316e..1bb8a6938 100644
--- a/ImperatorToCK3/CK3/Titles/Title.cs
+++ b/ImperatorToCK3/CK3/Titles/Title.cs
@@ -851,10 +851,10 @@ public void SetDeFactoLiege(Title? newLiege, Date date) {
 	}
 
 	[SerializeOnlyValue] public TitleCollection DeJureVassals { get; } = new(); // DIRECT de jure vassals
-	public Dictionary<string, Title> GetDeJureVassalsAndBelow() {
+	public IDictionary<string, Title> GetDeJureVassalsAndBelow() {
 		return GetDeJureVassalsAndBelow("bcdke");
 	}
-	public Dictionary<string, Title> GetDeJureVassalsAndBelow(string rankFilter) {
+	public IDictionary<string, Title> GetDeJureVassalsAndBelow(string rankFilter) {
 		var rankFilterAsArray = rankFilter.ToCharArray();
 		Dictionary<string, Title> deJureVassalsAndBelow = new();
 		foreach (var vassalTitle in DeJureVassals) {
@@ -874,14 +874,14 @@ public Dictionary<string, Title> GetDeJureVassalsAndBelow(string rankFilter) {
 
 		return deJureVassalsAndBelow;
 	}
-	public Dictionary<string, Title> GetDeFactoVassals(Date date) { // DIRECT de facto vassals
+	public IDictionary<string, Title> GetDeFactoVassals(Date date) { // DIRECT de facto vassals
 		return parentCollection.Where(t => t.GetDeFactoLiege(date)?.Id == Id)
 			.ToDictionary(t => t.Id, t => t);
 	}
-	public Dictionary<string, Title> GetDeFactoVassalsAndBelow(Date date) {
+	public IDictionary<string, Title> GetDeFactoVassalsAndBelow(Date date) {
 		return GetDeFactoVassalsAndBelow(date, "bcdke");
 	}
-	public Dictionary<string, Title> GetDeFactoVassalsAndBelow(Date date, string rankFilter) {
+	public IDictionary<string, Title> GetDeFactoVassalsAndBelow(Date date, string rankFilter) {
 		var rankFilterAsArray = rankFilter.ToCharArray();
 		Dictionary<string, Title> deFactoVassalsAndBelow = new();
 		foreach (var (vassalTitleName, vassalTitle) in GetDeFactoVassals(date)) {
@@ -1052,7 +1052,7 @@ public void OutputHistory(StreamWriter writer) {
 		writer.Write(sb);
 	}
 
-	public HashSet<ulong> GetProvincesInCountry(Date date) {
+	public ISet<ulong> GetProvincesInCountry(Date date) {
 		var holderId = GetHolderId(date);
 		var heldCounties = new List<Title>(
 			parentCollection.Where(t => t.GetHolderId(date) == holderId && t.Rank == TitleRank.county)
diff --git a/ImperatorToCK3/Outputter/BookmarkOutputter.cs b/ImperatorToCK3/Outputter/BookmarkOutputter.cs
index f6ff9b143..cad7d89a1 100644
--- a/ImperatorToCK3/Outputter/BookmarkOutputter.cs
+++ b/ImperatorToCK3/Outputter/BookmarkOutputter.cs
@@ -208,7 +208,7 @@ private static void DrawBookmarkMap(Configuration config, List<Title> playerTitl
 		foreach (var playerTitle in playerTitles) {
 			var colorOnMap = playerTitle.Color1 ?? new commonItems.Colors.Color(0, 0, 0);
 			var rgba32ColorOnMap = new Rgba32((byte)colorOnMap.R, (byte)colorOnMap.G, (byte)colorOnMap.B);
-			HashSet<ulong> heldProvinces = playerTitle.GetProvincesInCountry(config.CK3BookmarkDate);
+			ISet<ulong> heldProvinces = playerTitle.GetProvincesInCountry(config.CK3BookmarkDate);
 			// Determine which impassables should be be colored by the country
 			var provincesToColor = new HashSet<ulong>(heldProvinces);
 			var impassables = mapData.ColorableImpassableProvinces;