diff --git a/src/DebugSystem.cs b/src/DebugSystem.cs
index de9027a..fcffd9e 100644
--- a/src/DebugSystem.cs
+++ b/src/DebugSystem.cs
@@ -13,12 +13,9 @@ namespace MoonTools.ECS
 		{
 		}
 
-		protected IEnumerable<dynamic> Debug_GetAllComponents(Entity entity)
+		protected ComponentEnumerator Debug_GetAllComponents(Entity entity)
 		{
-			foreach (var typeIndex in EntityStorage.ComponentTypeIndices(entity.ID))
-			{
-				yield return ComponentDepot.Debug_Get(entity.ID, typeIndex);
-			}
+			return new ComponentEnumerator(ComponentDepot, entity, EntityStorage.ComponentTypeIndices(entity.ID));
 		}
 
 		protected IEnumerable<Entity> Debug_GetEntities(Type componentType)
@@ -39,6 +36,28 @@ namespace MoonTools.ECS
 				}
 			}
 		}
+
+		public ref struct ComponentEnumerator
+		{
+			private ComponentDepot ComponentDepot;
+			private Entity Entity;
+			private ReverseSpanEnumerator<int> ComponentTypeIndices;
+
+			public ComponentEnumerator GetEnumerator() => this;
+
+			internal ComponentEnumerator(
+				ComponentDepot componentDepot,
+				Entity entity,
+				Collections.IndexableSet<int> componentTypeIndices
+			) {
+				ComponentDepot = componentDepot;
+				Entity = entity;
+				ComponentTypeIndices = componentTypeIndices.GetEnumerator();
+			}
+
+			public bool MoveNext() => ComponentTypeIndices.MoveNext();
+			public object Current => ComponentDepot.Debug_Get(Entity.ID, ComponentTypeIndices.Current);
+		}
 	}
 }
 #endif
diff --git a/src/EntityStorage.cs b/src/EntityStorage.cs
index b73ad05..3ff05de 100644
--- a/src/EntityStorage.cs
+++ b/src/EntityStorage.cs
@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using MoonTools.ECS.Collections;
 
 namespace MoonTools.ECS
 {
@@ -10,8 +11,8 @@ namespace MoonTools.ECS
 		// FIXME: this is only needed in debug mode
 		private readonly HashSet<int> availableIDHash = new HashSet<int>();
 
-		private Dictionary<int, HashSet<int>> EntityToComponentTypeIndices = new Dictionary<int, HashSet<int>>();
-		private Dictionary<int, HashSet<int>> EntityToRelationTypeIndices = new Dictionary<int, HashSet<int>>();
+		private Dictionary<int, IndexableSet<int>> EntityToComponentTypeIndices = new Dictionary<int, IndexableSet<int>>();
+		private Dictionary<int, IndexableSet<int>> EntityToRelationTypeIndices = new Dictionary<int, IndexableSet<int>>();
 
 		public int Count => nextID - availableIDs.Count;
 
@@ -23,12 +24,12 @@ namespace MoonTools.ECS
 
 			if (!EntityToComponentTypeIndices.ContainsKey(entity.ID))
 			{
-				EntityToComponentTypeIndices.Add(entity.ID, new HashSet<int>());
+				EntityToComponentTypeIndices.Add(entity.ID, new IndexableSet<int>());
 			}
 
 			if (!EntityToRelationTypeIndices.ContainsKey(entity.ID))
 			{
-				EntityToRelationTypeIndices.Add(entity.ID, new HashSet<int>());
+				EntityToRelationTypeIndices.Add(entity.ID, new IndexableSet<int>());
 			}
 
 			Tags[entity.ID] = tag;
@@ -86,12 +87,12 @@ namespace MoonTools.ECS
 			return Tags[entityID];
 		}
 
-		public HashSet<int> ComponentTypeIndices(int entityID)
+		public IndexableSet<int> ComponentTypeIndices(int entityID)
 		{
 			return EntityToComponentTypeIndices[entityID];
 		}
 
-		public HashSet<int> RelationTypeIndices(int entityID)
+		public IndexableSet<int> RelationTypeIndices(int entityID)
 		{
 			return EntityToRelationTypeIndices[entityID];
 		}
diff --git a/src/FilterSignature.cs b/src/FilterSignature.cs
index f0eeaba..7e94922 100644
--- a/src/FilterSignature.cs
+++ b/src/FilterSignature.cs
@@ -22,8 +22,6 @@ namespace MoonTools.ECS
 
 		public bool Equals(FilterSignature other)
 		{
-			// workaround for HashSet<T>.SetEquals generating garbage
-			// maybe fixed in .NET 8?
 			foreach (var included in Included)
 			{
 				if (!other.Included.Contains(included))
diff --git a/src/FilterStorage.cs b/src/FilterStorage.cs
index 3cdf170..9d10c2c 100644
--- a/src/FilterStorage.cs
+++ b/src/FilterStorage.cs
@@ -148,10 +148,12 @@ namespace MoonTools.ECS
 				}
 			}
 
-			filterSignatureToEntityIDs[filterSignature].Add(entityID);
-			if (addCallbacks.TryGetValue(filterSignature, out var addCallback))
+			if (filterSignatureToEntityIDs[filterSignature].Add(entityID))
 			{
-				addCallback(entityID);
+				if (addCallbacks.TryGetValue(filterSignature, out var addCallback))
+				{
+					addCallback(entityID);
+				}
 			}
 		}