diff --git a/src/gl/scene/gl_portal.cpp b/src/gl/scene/gl_portal.cpp
index f165de630..be25409e2 100644
--- a/src/gl/scene/gl_portal.cpp
+++ b/src/gl/scene/gl_portal.cpp
@@ -825,7 +825,28 @@ void GLPlaneMirrorPortal::PopState()
 //
 //-----------------------------------------------------------------------------
 
+void GLLinePortal::PushState()
+{
+	FStateVec4 &v = gl_RenderState.GetClipLine();
+	planestack.Push(v.vec[0]);
+	planestack.Push(v.vec[1]);
+	planestack.Push(v.vec[2]);
+	planestack.Push(v.vec[3]);
+	planestack.Push(gl_RenderState.GetClipLineState());
+	gl_RenderState.EnableClipLine(false);
+}
 
+void GLLinePortal::PopState()
+{
+	FStateVec4 &v = gl_RenderState.GetClipLine();
+	float e;
+	planestack.Pop(e);
+	planestack.Pop(v.vec[3]);
+	planestack.Pop(v.vec[2]);
+	planestack.Pop(v.vec[1]);
+	planestack.Pop(v.vec[0]);
+	gl_RenderState.EnableClipLine(e != 0);
+}
 
 int GLLinePortal::ClipSeg(seg_t *seg) 
 { 
@@ -948,7 +969,10 @@ void GLMirrorPortal::DrawContents()
 	angle_t a1 = linedef->v2->GetClipAngle();
 	clipper.SafeAddClipRange(a1,a2);
 
+	gl_RenderState.SetClipLine(linedef);
+	gl_RenderState.EnableClipLine(true);
 	GLRenderer->DrawScene();
+	gl_RenderState.EnableClipLine(false);
 
 	MirrorFlag--;
 }
@@ -1018,7 +1042,10 @@ void GLLineToLinePortal::DrawContents()
 	GLRenderer->SetupView(ViewPos.X, ViewPos.Y, ViewPos.Z, ViewAngle, !!(MirrorFlag&1), !!(PlaneMirrorFlag&1));
 
 	ClearClipper();
+	gl_RenderState.SetClipLine(glport->reference->mDestination);
+	gl_RenderState.EnableClipLine(true);
 	GLRenderer->DrawScene();
+	gl_RenderState.EnableClipLine(false);
 	RestoreMapSection();
 }
 
diff --git a/src/gl/scene/gl_portal.h b/src/gl/scene/gl_portal.h
index 870009845..2962a4be1 100644
--- a/src/gl/scene/gl_portal.h
+++ b/src/gl/scene/gl_portal.h
@@ -225,6 +225,8 @@ struct GLLinePortal : public GLPortal
 	virtual int ClipSubsector(subsector_t *sub);
 	virtual int ClipPoint(const DVector2 &pos);
 	virtual bool NeedCap() { return false; }
+	virtual void PushState();
+	virtual void PopState();
 };
 
 
diff --git a/wadsrc/static/shaders/glsl/main.vp b/wadsrc/static/shaders/glsl/main.vp
index 44aec6199..7cc4d4d83 100644
--- a/wadsrc/static/shaders/glsl/main.vp
+++ b/wadsrc/static/shaders/glsl/main.vp
@@ -55,11 +55,15 @@ void main()
 	#endif
 	
 	
-	// clip planes used for reflective flats
-	if (uClipHeightDirection != 0.0)
+	
+	if (uClipHeightDirection != 0.0) // clip planes used for reflective flats
 	{
 		gl_ClipDistance[0] = (worldcoord.y - uClipHeight) * uClipHeightDirection;
 	}
+	else if (uClipLine.x > -1000000.0) // and for line portals - this will never be active at the same time as the reflective planes clipping so it can use the same hardware clip plane.
+	{
+		gl_ClipDistance[0] = -( (worldcoord.z - uClipLine.y) * uClipLine.z + (uClipLine.x - worldcoord.x) * uClipLine.w ) + 1.0/32768.0;	// allow a tiny bit of imprecisions for colinear linedefs.
+	}
 
 	// clip planes used for translucency splitting
 	gl_ClipDistance[1] = worldcoord.y - uClipSplit.x;