diff --git a/src/actionspecials.h b/src/actionspecials.h
index 9ee03d477..5405b2542 100644
--- a/src/actionspecials.h
+++ b/src/actionspecials.h
@@ -106,7 +106,7 @@ DEFINE_SPECIAL(Light_Glow, 114, 4, 4, 4)
 DEFINE_SPECIAL(Light_Flicker, 115, 3, 3, 3)
 DEFINE_SPECIAL(Light_Strobe, 116, 5, 5, 5)
 DEFINE_SPECIAL(Light_Stop, 117, 1, 1, 1)
-
+DEFINE_SPECIAL(Plane_Copy, 118, -1, -1, 5)
 DEFINE_SPECIAL(Thing_Damage, 119, 2, 3, 3)
 DEFINE_SPECIAL(Radius_Quake, 120, 5, 5, 5)  // Earthquake
 DEFINE_SPECIAL(Line_SetIdentification, 121, -1, -1, 5)
diff --git a/src/p_lnspec.cpp b/src/p_lnspec.cpp
index 818de725a..db2214ec7 100644
--- a/src/p_lnspec.cpp
+++ b/src/p_lnspec.cpp
@@ -3088,7 +3088,7 @@ lnSpecFunc LineSpecials[256] =
 	/* 115 */ LS_Light_Flicker,
 	/* 116 */ LS_Light_Strobe,
 	/* 117 */ LS_Light_Stop,
-	/* 118 */ LS_NOP,
+	/* 118 */ LS_NOP,		// Plane_Copy
 	/* 119 */ LS_Thing_Damage,
 	/* 120 */ LS_Radius_Quake,
 	/* 121 */ LS_NOP,		// Line_SetIdentification
@@ -3111,22 +3111,22 @@ lnSpecFunc LineSpecials[256] =
 	/* 138 */ LS_Floor_Waggle,
 	/* 139 */ LS_Thing_SpawnFacing,
 	/* 140 */ LS_Sector_ChangeSound,
-	/* 141 */ LS_NOP,		// 141 Music_Pause			// [BC] Start
-	/* 142 */ LS_NOP,		// 142 Music_Change
-	/* 143 */ LS_NOP,		// 143 Player_RemoveItem
-	/* 144 */ LS_NOP,		// 144 Player_GiveItem
+	/* 141 */ LS_NOP,
+	/* 142 */ LS_NOP,
+	/* 143 */ LS_NOP,
+	/* 144 */ LS_NOP,
 	/* 145 */ LS_NOP,		// 145 Player_SetTeam
-	/* 146 */ LS_NOP,		// 146 Player_SetLeader
-	/* 147 */ LS_NOP,		// 147 Team_InitFP
-	/* 148 */ LS_NOP,		// 148 TeleportAll
-	/* 149 */ LS_NOP,		// 149 TeleportAll_NoFog
-	/* 150 */ LS_NOP,		// 150 Team_GiveFP
-	/* 151 */ LS_NOP,		// 151 Team_UseFP
+	/* 146 */ LS_NOP,
+	/* 147 */ LS_NOP,
+	/* 148 */ LS_NOP,
+	/* 149 */ LS_NOP,
+	/* 150 */ LS_NOP,
+	/* 151 */ LS_NOP,
 	/* 152 */ LS_NOP,		// 152 Team_Score
-	/* 153 */ LS_NOP,		// 153 Team_Init
+	/* 153 */ LS_NOP,		// 153 Team_GivePoints
 	/* 154 */ LS_Teleport_NoStop,
-	/* 155 */ LS_NOP,		// 155 Team_RemoveItem
-	/* 156 */ LS_NOP,		// 156 Team_GiveItem		// [BC] End
+	/* 155 */ LS_NOP,
+	/* 156 */ LS_NOP,
 	/* 157 */ LS_NOP,		// SetGlobalFogParameter // in GZDoom
 	/* 158 */ LS_NOP,		// FS_Execute in GZDoom
 	/* 159 */ LS_NOP,		// Sector_SetPlaneReflection in GZDoom
diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index 85c958a1d..202cca409 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -68,6 +68,7 @@
 
 void P_SpawnSlopeMakers (FMapThing *firstmt, FMapThing *lastmt);
 void P_SetSlopes ();
+void P_CopySlopes();
 void BloodCrypt (void *data, int key, int len);
 void P_ClearUDMFKeys();
 
@@ -3628,6 +3629,7 @@ void P_SetupLevel (char *lumpname, int position)
 	{
 		// [RH] Spawn slope creating things first.
 		P_SpawnSlopeMakers (&MapThingsConverted[0], &MapThingsConverted[MapThingsConverted.Size()]);
+		P_CopySlopes();
 
 		// Spawn 3d floors - must be done before spawning things so it can't be done in P_SpawnSpecials
 		P_Spawn3DFloors();
diff --git a/src/p_slopes.cpp b/src/p_slopes.cpp
index 99dcb71b2..3ebaef144 100644
--- a/src/p_slopes.cpp
+++ b/src/p_slopes.cpp
@@ -118,9 +118,8 @@ static void P_SlopeLineToPoint (int lineid, fixed_t x, fixed_t y, fixed_t z, boo
 //
 //===========================================================================
 
-static void P_CopyPlane (int tag, fixed_t x, fixed_t y, bool copyCeil)
+static void P_CopyPlane (int tag, sector_t *dest, bool copyCeil)
 {
-	sector_t *dest = P_PointInSector (x, y);
 	sector_t *source;
 	int secnum;
 	size_t planeofs;
@@ -144,6 +143,12 @@ static void P_CopyPlane (int tag, fixed_t x, fixed_t y, bool copyCeil)
 	*(secplane_t *)((BYTE *)dest + planeofs) = *(secplane_t *)((BYTE *)source + planeofs);
 }
 
+static void P_CopyPlane (int tag, fixed_t x, fixed_t y, bool copyCeil)
+{
+	sector_t *dest = P_PointInSector (x, y);
+	P_CopyPlane(tag, dest, copyCeil);
+}
+
 //===========================================================================
 //
 // P_SetSlope
@@ -571,3 +576,52 @@ void P_SetSlopes ()
 	}
 }
 
+//===========================================================================
+//
+// P_CopySlopes
+//
+//===========================================================================
+
+void P_CopySlopes()
+{
+	for (int i = 0; i < numlines; i++)
+	{
+		if (lines[i].special == Plane_Copy)
+		{
+			// The args are used for the tags of sectors to copy:
+			// args[0]: front floor
+			// args[1]: front ceiling
+			// args[2]: back floor
+			// args[3]: back ceiling
+			// args[4]: copy slopes from one side of the line to the other.
+			lines[i].special = 0;
+			for (int s = 0; s < (lines[i].backsector ? 4 : 2); s++)
+			{
+				if (lines[i].args[s])
+					P_CopyPlane(lines[i].args[s], 
+					(s & 2 ? lines[i].backsector : lines[i].frontsector), s & 1);
+			}
+
+			if (lines[i].backsector != NULL)
+			{
+				if ((lines[i].args[4] & 3) == 1)
+				{
+					lines[i].backsector->floorplane = lines[i].frontsector->floorplane;
+				}
+				else if ((lines[i].args[4] & 3) == 2)
+				{
+					lines[i].frontsector->floorplane = lines[i].backsector->floorplane;
+				}
+				if ((lines[i].args[4] & 12) == 4)
+				{
+					lines[i].backsector->ceilingplane = lines[i].frontsector->ceilingplane;
+				}
+				else if ((lines[i].args[4] & 12) == 8)
+				{
+					lines[i].frontsector->ceilingplane = lines[i].backsector->ceilingplane;
+				}
+			}
+		}
+	}
+}
+