diff --git a/Source/MaterialDef.cs b/Source/MaterialDef.cs
index 18e5e9c..3ac5e1f 100644
--- a/Source/MaterialDef.cs
+++ b/Source/MaterialDef.cs
@@ -65,11 +65,11 @@ public class MaterialDef
 
 	[Persistent] public bool preserveRenderQueue = false;
 
-	public Dictionary<string, bool> keywords;
-	public Dictionary<string, float> floats;
-	public Dictionary<string, Color> colors;
-	public Dictionary<string, Vector4> vectors;
-	public Dictionary<string, string> textureNames;
+	public readonly Dictionary<string, bool> keywords;
+	public readonly Dictionary<string, float> floats;
+	public readonly Dictionary<string, Color> colors;
+	public readonly Dictionary<string, Vector4> vectors;
+	public readonly Dictionary<string, string> textureNames;
 
 	readonly Dictionary<string, Texture> textures = new Dictionary<string, Texture>();
 
diff --git a/Source/MaterialReplacement.cs b/Source/MaterialReplacement.cs
index 2cd7614..897087c 100644
--- a/Source/MaterialReplacement.cs
+++ b/Source/MaterialReplacement.cs
@@ -26,7 +26,7 @@ namespace Shabby
 
 public class MaterialReplacement : ModelFilter
 {
-	public MaterialDef materialDef = null;
+	public readonly MaterialDef materialDef = null;
 	readonly Dictionary<Material, Material> replacedMaterials = new Dictionary<Material, Material>();
 
 	public MaterialReplacement(ConfigNode node) : base(node)
diff --git a/Source/ModelFilter.cs b/Source/ModelFilter.cs
index da79653..02f28ae 100644
--- a/Source/ModelFilter.cs
+++ b/Source/ModelFilter.cs
@@ -24,11 +24,11 @@ namespace Shabby
 {
 public class ModelFilter
 {
-	public HashSet<string> targetMaterials;
-	public HashSet<string> targetTransforms;
-	public bool blanketApply;
+	public readonly HashSet<string> targetMaterials;
+	public readonly HashSet<string> targetTransforms;
+	public readonly bool blanketApply;
 
-	public HashSet<string> ignoredMeshes;
+	public readonly HashSet<string> ignoredMeshes;
 
 	public ModelFilter(ConfigNode node)
 	{