diff --git a/src/gl/scene/gl_walls.cpp b/src/gl/scene/gl_walls.cpp
index 3acf209a6..89eb1d67f 100644
--- a/src/gl/scene/gl_walls.cpp
+++ b/src/gl/scene/gl_walls.cpp
@@ -1547,7 +1547,7 @@ void GLWall::Process(seg_t *seg, sector_t * frontsector, sector_t * backsector)
 			zbottom[1] = zfloor[1];
 			PutPortal(PORTALTYPE_LINETOLINE);
 		}
-		else if (seg->linedef->portaltransferred > 0)
+		else if (seg->linedef->GetTransferredPortal())
 		{
 			SkyLine(frontsector, seg->linedef);
 		}
diff --git a/src/p_sectors.cpp b/src/p_sectors.cpp
index ef28af020..3d77b44c9 100644
--- a/src/p_sectors.cpp
+++ b/src/p_sectors.cpp
@@ -1772,6 +1772,19 @@ DEFINE_ACTION_FUNCTION(_Sector, NextLowestFloorAt)
 	 ACTION_RETURN_FLOAT(self->CenterCeiling());
  }
 
+ DEFINE_ACTION_FUNCTION(_Sector, Index)
+ {
+	PARAM_SELF_STRUCT_PROLOGUE(sector_t);
+	unsigned ndx = self->Index();
+	if (ndx >= level.sectors.Size())
+	{
+		// This qualifies as an array out of bounds exception. Normally it can only happen when a sector copy is concerned which scripts should not be able to create.
+		va_list ap;
+		throw CVMAbortException(X_ARRAY_OUT_OF_BOUNDS, "Accessed invalid sector", ap);
+	}
+	ACTION_RETURN_INT(ndx);
+ }
+
 //===========================================================================
 //
 // 
@@ -2100,6 +2113,7 @@ DEFINE_FIELD_X(Line, line_t, backsector)
 DEFINE_FIELD_X(Line, line_t, validcount)
 DEFINE_FIELD_X(Line, line_t, locknumber)
 DEFINE_FIELD_X(Line, line_t, portalindex)
+DEFINE_FIELD_X(Line, line_t, portaltransferred)
 
 DEFINE_FIELD_X(Secplane, secplane_t, normal)
 DEFINE_FIELD_X(Secplane, secplane_t, D)
diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index d81376abe..10f4265d3 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -2156,6 +2156,7 @@ void P_LoadLineDefs (MapData * map)
 	{
 		ld->alpha = 1.;	// [RH] Opaque by default
 		ld->portalindex = UINT_MAX;
+		ld->portaltransferred = UINT_MAX;
 
 		// [RH] Translate old linedef special and flags to be
 		//		compatible with the new format.
@@ -2249,6 +2250,7 @@ void P_LoadLineDefs2 (MapData * map)
 		int j;
 
 		ld->portalindex = UINT_MAX;
+		ld->portaltransferred = UINT_MAX;
 
 		for (j = 0; j < 5; j++)
 			ld->args[j] = mld->args[j];
diff --git a/src/p_udmf.cpp b/src/p_udmf.cpp
index ba9805b1c..8e88fc89d 100644
--- a/src/p_udmf.cpp
+++ b/src/p_udmf.cpp
@@ -1824,6 +1824,9 @@ public:
 		{
 			short tempalpha[2] = { SHRT_MIN, SHRT_MIN };
 
+			lines[line].portalindex = UINT_MAX;
+			lines[line].portaltransferred = UINT_MAX;
+
 			lines[line] = ParsedLines[line];
 
 			for(int sd = 0; sd < 2; sd++)
diff --git a/wadsrc/static/zscript/base.txt b/wadsrc/static/zscript/base.txt
index 673257a3c..b48f0ee58 100644
--- a/wadsrc/static/zscript/base.txt
+++ b/wadsrc/static/zscript/base.txt
@@ -226,7 +226,7 @@ struct Line native
 	};
 
 
-	//native readonly vertex		v1, v2;		// vertices, from v1 to v2
+	native readonly vertex			v1, v2;		// vertices, from v1 to v2
 	native readonly Vector2			delta;		// precalculated v2 - v1 for side checking
 	native uint						flags;
 	native uint						activation;	// activation type
@@ -239,6 +239,7 @@ struct Line native
 	native int 						validcount;	// if == validcount, already checked
 	native int						locknumber;	// [Dusk] lock number for special
 	native readonly uint			portalindex;
+	native readonly uint			portaltransferred;
 }
 
 struct SecPlane native
@@ -378,6 +379,7 @@ struct Sector native
 
 	native readonly int			sectornum;
 
+	native int Index();
 
 	native double, Sector, F3DFloor NextHighestCeilingAt(double x, double y, double bottomz, double topz, int flags = 0);
 	native double, Sector, F3DFloor NextLowestFloorAt(double x, double y, double z, int flags = 0, double steph = 0);