diff --git a/wadsrc/static/zscript/actors/actor.zs b/wadsrc/static/zscript/actors/actor.zs
index 20659551c..c3b70460d 100644
--- a/wadsrc/static/zscript/actors/actor.zs
+++ b/wadsrc/static/zscript/actors/actor.zs
@@ -63,8 +63,8 @@ struct FLineTraceData
 
 struct LinkContext
 {
-	voidptr sector_list;	// really msecnode but that's not exported yet.
-	voidptr render_list;
+	readonly voidptr sector_list;	// really msecnode but that's not exported yet.
+	readonly voidptr render_list;
 }
 
 class ViewPosition native
@@ -265,7 +265,7 @@ class Actor : Thinker native
 	native readonly State SeeState;
 	native State MeleeState;
 	native State MissileState;
-	native voidptr /*DecalBase*/ DecalGenerator;
+	native readonly internal voidptr /*DecalBase*/ DecalGenerator;
 	native uint8 fountaincolor;
 	native double CameraHeight;	// Height of camera when used as such
 	native double CameraFOV;
diff --git a/wadsrc/static/zscript/engine/base.zs b/wadsrc/static/zscript/engine/base.zs
index d182f5234..75f95ee26 100644
--- a/wadsrc/static/zscript/engine/base.zs
+++ b/wadsrc/static/zscript/engine/base.zs
@@ -263,7 +263,7 @@ struct MusPlayingInfo native
 	native String name;
 	native int baseorder;
 	native bool loop;
-	native voidptr handle;
+	native readonly voidptr handle;
 	
 };
 
@@ -987,7 +987,7 @@ struct QuatStruct native unsafe(internal)
 
 struct ScriptSavedPos
 {
-	voidptr SavedScriptPtr;
+	readonly voidptr SavedScriptPtr;
 	int SavedScriptLine;
 }
 
diff --git a/wadsrc/static/zscript/engine/ui/menu/messagebox.zs b/wadsrc/static/zscript/engine/ui/menu/messagebox.zs
index a49ff6f3f..52734cf04 100644
--- a/wadsrc/static/zscript/engine/ui/menu/messagebox.zs
+++ b/wadsrc/static/zscript/engine/ui/menu/messagebox.zs
@@ -35,7 +35,7 @@
 class MessageBoxMenu : Menu
 {
 	BrokenLines mMessage;
-	voidptr Handler;
+	readonly internal voidptr Handler;
 	int mMessageMode;
 	int messageSelection;
 	int mMouseLeft, mMouseRight, mMouseY;
@@ -45,7 +45,7 @@ class MessageBoxMenu : Menu
 	int destWidth, destHeight;
 	String selector;
 
-	native static void CallHandler(voidptr hnd);
+	private native static void CallHandler(voidptr hnd);
 
 
 	//=============================================================================