diff --git a/src/scripting/thingdef_data.cpp b/src/scripting/thingdef_data.cpp
index c50b7f65b..a09134d58 100644
--- a/src/scripting/thingdef_data.cpp
+++ b/src/scripting/thingdef_data.cpp
@@ -858,8 +858,8 @@ void InitThingdef()
 	// As a result, the size has to be set to something large and arbritrary because it can change between maps. This will need some serious improvement when things get cleaned up.
 	sectorstruct->AddNativeField("lines", NewPointer(NewResizableArray(NewPointer(linestruct, false)), false), myoffsetof(sector_t, Lines), VARF_Native);
 
-	sectorstruct->AddNativeField("ceilingplane", secplanestruct, myoffsetof(sector_t, ceilingplane), VARF_Native);
-	sectorstruct->AddNativeField("floorplane", secplanestruct, myoffsetof(sector_t, floorplane), VARF_Native);
+	sectorstruct->AddNativeField("ceilingplane", secplanestruct, myoffsetof(sector_t, ceilingplane), VARF_Native | VARF_ReadOnly);
+	sectorstruct->AddNativeField("floorplane", secplanestruct, myoffsetof(sector_t, floorplane), VARF_Native | VARF_ReadOnly);
 
 
 
diff --git a/wadsrc/static/zscript/base.txt b/wadsrc/static/zscript/base.txt
index 2c1fb6661..a15b78de8 100644
--- a/wadsrc/static/zscript/base.txt
+++ b/wadsrc/static/zscript/base.txt
@@ -386,7 +386,6 @@ class Thinker : Object native play
 
 class ThinkerIterator : Object native
 {
-
 	native static ThinkerIterator Create(class<Object> type = "Actor", int statnum=Thinker.MAX_STATNUM+1);
 	native Thinker Next(bool exact = false);
 	native void Reinit();
diff --git a/wadsrc/static/zscript/mapdata.txt b/wadsrc/static/zscript/mapdata.txt
index 4bbfb7097..3d18f9f5e 100644
--- a/wadsrc/static/zscript/mapdata.txt
+++ b/wadsrc/static/zscript/mapdata.txt
@@ -143,7 +143,7 @@ struct Line native play
 	native int						special;
 	native int						args[5];	// <--- hexen-style arguments (expanded to ZDoom's full width)
 	native double					alpha;		// <--- translucency (0=invisibile, FRACUNIT=opaque)
-	native Side						sidedef[2];
+	native readonly Side			sidedef[2];
 	native readonly double			bbox[4];	// bounding box, for the extent of the LineDef.
 	native readonly Sector			frontsector, backsector;
 	native int 						validcount;	// if == validcount, already checked
@@ -177,15 +177,15 @@ struct SecPlane native play
 	native double D;
 	native double negiC;
 	
-	native bool isSlope();
-	native int PointOnSide(Vector3 pos);
-	native double ZatPoint (Vector2 v);
-	native double ZatPointDist(Vector2 v, double dist);
-	native bool isEqual(Secplane other);
+	native bool isSlope() const;
+	native int PointOnSide(Vector3 pos) const;
+	native double ZatPoint (Vector2 v) const;
+	native double ZatPointDist(Vector2 v, double dist) const;
+	native bool isEqual(Secplane other) const;
 	native void ChangeHeight(double hdiff);
-	native double GetChangedHeight(double hdiff);
+	native double GetChangedHeight(double hdiff) const;
 	native double HeightDiff(double oldd, double newd = 0.0);
-	native double PointToDist(Vector2 xy, double z);
+	native double PointToDist(Vector2 xy, double z) const;
 }
 
 // This encapsulates all info Doom's original 'special' field contained - for saving and transferring.