diff --git a/src/portal.cpp b/src/portal.cpp
index 055603d8c..1e3bf30a8 100644
--- a/src/portal.cpp
+++ b/src/portal.cpp
@@ -12,6 +12,7 @@ CVAR(Int, sv_portal_recursions, 4, CVAR_ARCHIVE|CVAR_SERVERINFO)
 
 PortalDrawseg* CurrentPortal = NULL;
 int CurrentPortalUniq = 0;
+bool CurrentPortalInSkybox = false;
 
 // [ZZ] lots of floats here to avoid overflowing a lot
 bool R_IntersectLines(fixed_t o1x, fixed_t o1y, fixed_t p1x, fixed_t p1y,
@@ -48,9 +49,14 @@ bool R_IntersectLines(fixed_t o1x, fixed_t o1y, fixed_t p1x, fixed_t p1y,
 	return true;
 }
 
+inline int P_PointOnLineSideExplicit (fixed_t x, fixed_t y, fixed_t x1, fixed_t y1, fixed_t x2, fixed_t y2)
+{
+	return DMulScale32 (y-y1, x2-x1, x1-x, y2-y1) > 0;
+}
+
 bool P_ClipLineToPortal(line_t* line, line_t* portal, fixed_t viewx, fixed_t viewy, bool partial, bool samebehind)
 {
-	// we do this only if simple check doesn't clip away the line
+	// check if this line is between portal and the viewer. clip away if it is.
 	bool behind1 = !!P_PointOnLineSide(line->v1->x, line->v1->y, portal);
 	bool behind2 = !!P_PointOnLineSide(line->v2->x, line->v2->y, portal);
 
@@ -64,41 +70,12 @@ bool P_ClipLineToPortal(line_t* line, line_t* portal, fixed_t viewx, fixed_t vie
 			behind2 = samebehind;
 
 	if (behind1 && behind2)
-		return true;
-
-	if ((behind1 || behind2) && partial)
 	{
-		fixed_t v1x = line->v1->x;
-		fixed_t v1y = line->v1->y;
-		fixed_t v2x = line->v2->x;
-		fixed_t v2y = line->v2->y;
-
-		fixed_t check1X = viewx;
-		fixed_t check1Y = viewy;
-
-		fixed_t check2X = portal->v2->x;
-		fixed_t check2Y = portal->v2->y;
-
-		fixed_t in1x = v1x;
-		fixed_t in1y = v1y;
-
-		bool i1 = R_IntersectLines(check1X, check1Y, check2X, check2Y, v1x, v1y, v2x, v2y, in1x, in1y);
-
-		check2X = portal->v1->x;
-		check2Y = portal->v1->y;
-
-		fixed_t in2x = v2x;
-		fixed_t in2y = v2y;
-
-		bool i2 = R_IntersectLines(check1X, check1Y, check2X, check2Y, v1x, v1y, v2x, v2y, in2x, in2y);
-
-		//if (log) Printf("intersection = %d [at %.2f, %.2f]; %d [at %.2f, %.2f]\n", i1, FIXED2FLOAT(in1x), FIXED2FLOAT(in1y), i2, FIXED2FLOAT(in2x), FIXED2FLOAT(in2y));
-
-		// now, to cull the shitty line that obstructs the view, we check if any of intersected points are on behind of the portal :)
-		behind1 = !!P_PointOnLineSide(in1x, in1y, portal);
-		behind2 = !!P_PointOnLineSide(in2x, in2y, portal);
-
-		if (behind1 && behind2)
+		// line is behind the portal plane. now check if it's in front of two view plane borders (i.e. if it will get in the way of rendering)
+		fixed_t dummyx, dummyy;
+		bool infront1 = R_IntersectLines(line->v1->x, line->v1->y, line->v2->x, line->v2->y, viewx, viewy, portal->v1->x, portal->v1->y, dummyx, dummyy);
+		bool infront2 = R_IntersectLines(line->v1->x, line->v1->y, line->v2->x, line->v2->y, viewx, viewy, portal->v2->x, portal->v2->y, dummyx, dummyy);
+		if (infront1 && infront2)
 			return true;
 	}
 
diff --git a/src/portal.h b/src/portal.h
index 5897622fd..103e3072b 100644
--- a/src/portal.h
+++ b/src/portal.h
@@ -26,6 +26,7 @@ struct PortalDrawseg
 
 extern PortalDrawseg* CurrentPortal;
 extern int CurrentPortalUniq;
+extern bool CurrentPortalInSkybox;
 
 /* code ported from prototype */
 bool P_ClipLineToPortal(line_t* line, line_t* portal, fixed_t viewx, fixed_t viewy, bool partial = true, bool samebehind = true);
diff --git a/src/r_bsp.cpp b/src/r_bsp.cpp
index 5605272e7..8a7e5c560 100644
--- a/src/r_bsp.cpp
+++ b/src/r_bsp.cpp
@@ -555,7 +555,8 @@ void R_AddLine (seg_t *line)
 	}
 
 	// reject lines that aren't seen from the portal (if any)
-	if (CurrentPortal && P_ClipLineToPortal(line->linedef, CurrentPortal->dst, viewx, viewy))
+	// [ZZ] 10.01.2016: lines inside a skybox shouldn't be clipped, although this imposes some limitations on portals in skyboxes.
+	if (!CurrentPortalInSkybox && CurrentPortal && P_ClipLineToPortal(line->linedef, CurrentPortal->dst, viewx, viewy))
 		return;
 
 	vertex_t *v1, *v2;
diff --git a/src/r_main.cpp b/src/r_main.cpp
index ef942734e..c0fe5819c 100644
--- a/src/r_main.cpp
+++ b/src/r_main.cpp
@@ -659,7 +659,7 @@ void R_HighlightPortal (PortalDrawseg* pds)
 void R_EnterPortal (PortalDrawseg* pds, int depth)
 {
 	// [ZZ] check depth. fill portal with black if it's exceeding the visual recursion limit, and continue like nothing happened.
-	if (depth > r_portal_recursions)
+	if (depth >= r_portal_recursions)
 	{
 		BYTE color = (BYTE)BestColor((DWORD *)GPalette.BaseColors, 0, 0, 0, 0, 255);
 		int spacing = RenderTarget->GetPitch();
diff --git a/src/r_plane.cpp b/src/r_plane.cpp
index 394a77993..ed013b821 100644
--- a/src/r_plane.cpp
+++ b/src/r_plane.cpp
@@ -1193,6 +1193,7 @@ void R_DrawSkyBoxes ()
 		return;
 
 	R_3D_EnterSkybox();
+	CurrentPortalInSkybox = true;
 
 	int savedextralight = extralight;
 	fixed_t savedx = viewx;
@@ -1367,6 +1368,7 @@ void R_DrawSkyBoxes ()
 	viewangle = savedangle;
 	R_SetViewAngle ();
 
+	CurrentPortalInSkybox = false;
 	R_3D_LeaveSkybox();
 
 	if(fakeActive) return;
diff --git a/src/r_things.cpp b/src/r_things.cpp
index 3a6773c70..9c3d5fe42 100644
--- a/src/r_things.cpp
+++ b/src/r_things.cpp
@@ -320,7 +320,7 @@ nextpost:
 // [ZZ]
 // R_ClipSpriteColumnWithPortals
 //
-bool R_ClipSpriteColumnWithPortals (fixed_t x, fixed_t y, vissprite_t* spr)
+static inline bool R_ClipSpriteColumnWithPortals (fixed_t x, fixed_t y, vissprite_t* spr)
 {
 	for (drawseg_t* seg = ds_p; seg-- > firstdrawseg; ) // copied code from killough below
 	{