diff --git a/src/gl/scene/gl_drawinfo.h b/src/gl/scene/gl_drawinfo.h
index 05ca3dd8d..1add3bf4d 100644
--- a/src/gl/scene/gl_drawinfo.h
+++ b/src/gl/scene/gl_drawinfo.h
@@ -121,6 +121,7 @@ struct FDrawInfo : public HWDrawInfo
 	void ProcessLights(GLFlat *flat, bool istrans);
 	void DrawSubsector(GLFlat *flat, subsector_t * sub);
 	void SetupSubsectorLights(GLFlat *flat, int pass, subsector_t * sub, int *dli);
+	void SetupSectorLights(GLFlat *flat, int pass, int *dli);
 
 	// Sprite drawer
 	void DrawSprite(GLSprite *sprite, int pass);
diff --git a/src/gl/scene/gl_flats.cpp b/src/gl/scene/gl_flats.cpp
index ac6415b43..d4105c569 100644
--- a/src/gl/scene/gl_flats.cpp
+++ b/src/gl/scene/gl_flats.cpp
@@ -62,7 +62,35 @@ void FDrawInfo::SetupSubsectorLights(GLFlat *flat, int pass, subsector_t * sub,
 		(*dli)++;
 		return;
 	}
-	if (flat->SetupSubsectorLights(pass, sub, lightdata))
+	if (flat->SetupSectorLights(pass, flat->sector, lightdata))
+	{
+		int d = GLRenderer->mLights->UploadLights(lightdata);
+		if (pass == GLPASS_LIGHTSONLY)
+		{
+			GLRenderer->mLights->StoreIndex(d);
+		}
+		else
+		{
+			gl_RenderState.ApplyLightIndex(d);
+		}
+	}
+}
+
+//==========================================================================
+//
+//
+//
+//==========================================================================
+
+void FDrawInfo::SetupSectorLights(GLFlat *flat, int pass, int *dli)
+{
+	if (dli != NULL && *dli != -1)
+	{
+		gl_RenderState.ApplyLightIndex(GLRenderer->mLights->GetIndex(*dli));
+		(*dli)++;
+		return;
+	}
+	if (flat->SetupSectorLights(pass, flat->sector, lightdata))
 	{
 		int d = GLRenderer->mLights->UploadLights(lightdata);
 		if (pass == GLPASS_LIGHTSONLY)
@@ -137,13 +165,20 @@ void FDrawInfo::ProcessLights(GLFlat *flat, bool istrans)
 {
 	flat->dynlightindex = GLRenderer->mLights->GetIndexPtr();
 
-	// Draw the subsectors belonging to this sector
-	for (int i=0; i< flat->sector->subsectorcount; i++)
+	if (flat->sector->ibocount > 0)
 	{
-		subsector_t * sub = flat->sector->subsectors[i];
-		if (gl_drawinfo->ss_renderflags[sub->Index()]& flat->renderflags || istrans)
+		SetupSectorLights(flat, GLPASS_LIGHTSONLY, nullptr);
+	}
+	else
+	{
+		// Draw the subsectors belonging to this sector
+		for (int i = 0; i < flat->sector->subsectorcount; i++)
 		{
-			SetupSubsectorLights(flat, GLPASS_LIGHTSONLY, sub, nullptr);
+			subsector_t * sub = flat->sector->subsectors[i];
+			if (gl_drawinfo->ss_renderflags[sub->Index()] & flat->renderflags || istrans)
+			{
+				SetupSubsectorLights(flat, GLPASS_LIGHTSONLY, sub, nullptr);
+			}
 		}
 	}
 
@@ -175,7 +210,18 @@ void FDrawInfo::DrawSubsectors(GLFlat *flat, int pass, bool processlights, bool
 
 	gl_RenderState.Apply();
 	if (gl.legacyMode) processlights = false;
-	if (flat->vboindex >= 0)
+
+	auto vcount = flat->sector->ibocount;
+	if (vcount > 0)
+	{
+		if (processlights) SetupSectorLights(flat, GLPASS_ALL, &dli);
+		drawcalls.Clock();
+		glDrawElements(GL_TRIANGLES, vcount, GL_UNSIGNED_INT, GLRenderer->mVBO->GetIndexPointer() + flat->vboindex);
+		drawcalls.Unclock();
+		flatvertices += vcount;
+		flatprimitives++;
+	}
+	else if (flat->vboindex >= 0)
 	{
 		int index = flat->vboindex;
 		for (int i=0; i<flat->sector->subsectorcount; i++)
diff --git a/src/hwrenderer/data/flatvertices.cpp b/src/hwrenderer/data/flatvertices.cpp
index 0fba9a50f..cba80b11a 100644
--- a/src/hwrenderer/data/flatvertices.cpp
+++ b/src/hwrenderer/data/flatvertices.cpp
@@ -165,6 +165,7 @@ int FFlatVertexGenerator::CreateIndexedSectorVertices(sector_t *sec, const secpl
 		subsector_t *sub = sec->subsectors[j];
 		CreateIndexedSubsectorVertices(sub, plane, floor, vi, gen);
 	}
+	sec->ibocount = ibo_data.Size() - rt;
 	return rt;
 }
 
diff --git a/src/hwrenderer/scene/hw_drawstructs.h b/src/hwrenderer/scene/hw_drawstructs.h
index 7aa7e0b7d..56c74a8f7 100644
--- a/src/hwrenderer/scene/hw_drawstructs.h
+++ b/src/hwrenderer/scene/hw_drawstructs.h
@@ -311,7 +311,9 @@ public:
 
 	int dynlightindex;
 
+	bool SetupLights(int pass, FLightNode *head, FDynLightData &lightdata, int portalgroup);
 	bool SetupSubsectorLights(int pass, subsector_t * sub, FDynLightData &lightdata);
+	bool SetupSectorLights(int pass, sector_t * sec, FDynLightData &lightdata);
 
 	void PutFlat(HWDrawInfo *di, bool fog = false);
 	void Process(HWDrawInfo *di, sector_t * model, int whichplane, bool notexture);
diff --git a/src/hwrenderer/scene/hw_flats.cpp b/src/hwrenderer/scene/hw_flats.cpp
index dabee535d..0aafadc26 100644
--- a/src/hwrenderer/scene/hw_flats.cpp
+++ b/src/hwrenderer/scene/hw_flats.cpp
@@ -92,14 +92,13 @@ bool hw_SetPlaneTextureRotation(const GLSectorPlane * secplane, FMaterial * glte
 //
 //==========================================================================
 
-bool GLFlat::SetupSubsectorLights(int pass, subsector_t * sub, FDynLightData &lightdata)
+bool GLFlat::SetupLights(int pass, FLightNode * node, FDynLightData &lightdata, int portalgroup)
 {
 	Plane p;
 
 	if (renderstyle == STYLE_Add && !level.lightadditivesurfaces) return false;	// no lights on additively blended surfaces.
 
 	lightdata.Clear();
-	FLightNode * node = sub->lighthead;
 	while (node)
 	{
 		ADynamicLight * light = node->lightsource;
@@ -121,13 +120,23 @@ bool GLFlat::SetupSubsectorLights(int pass, subsector_t * sub, FDynLightData &li
 		}
 
 		p.Set(plane.plane.Normal(), plane.plane.fD());
-		lightdata.GetLight(sub->sector->PortalGroup, p, light, false);
+		lightdata.GetLight(portalgroup, p, light, false);
 		node = node->nextLight;
 	}
 
 	return true;
 }
 
+bool GLFlat::SetupSubsectorLights(int pass, subsector_t * sub, FDynLightData &lightdata)
+{
+	return SetupLights(pass, sub->lighthead, lightdata, sub->sector->PortalGroup);
+}
+
+bool GLFlat::SetupSectorLights(int pass, sector_t * sec, FDynLightData &lightdata)
+{
+	return SetupLights(pass, sec->lighthead, lightdata, sec->PortalGroup);
+}
+
 //==========================================================================
 //
 // GLFlat::PutFlat
@@ -252,6 +261,7 @@ void GLFlat::ProcessSector(HWDrawInfo *di, sector_t * frontsector)
 	sector = &level.sectors[frontsector->sectornum];
 	extsector_t::xfloor &x = sector->e->XFloor;
 	dynlightindex = -1;
+	vertexcount = sector->ibocount;
 
 	uint8_t &srf = di->sectorrenderflags[sector->sectornum];
 
diff --git a/src/hwrenderer/scene/hw_renderhacks.cpp b/src/hwrenderer/scene/hw_renderhacks.cpp
index 5eacd9dfc..bfc7b38d3 100644
--- a/src/hwrenderer/scene/hw_renderhacks.cpp
+++ b/src/hwrenderer/scene/hw_renderhacks.cpp
@@ -1077,6 +1077,7 @@ void HWDrawInfo::ProcessSectorStacks(area_t in_area)
 				{				
 					subsector_t *sub = HandledSubsectors[j];
 					ss_renderflags[sub->Index()] &= ~SSRF_RENDERCEILING;
+					sub->sector->ibocount = -1;	// cannot render this sector in one go.
 
 					if (sub->portalcoverage[sector_t::ceiling].subsectors == NULL)
 					{
@@ -1122,6 +1123,7 @@ void HWDrawInfo::ProcessSectorStacks(area_t in_area)
 				{				
 					subsector_t *sub = HandledSubsectors[j];
 					ss_renderflags[sub->Index()] &= ~SSRF_RENDERFLOOR;
+					sub->sector->ibocount = -1;	// cannot render this sector in one go.
 
 					if (sub->portalcoverage[sector_t::floor].subsectors == NULL)
 					{