diff --git a/src/gl/data/gl_setup.cpp b/src/gl/data/gl_setup.cpp
index fc63cb95b5..5e6e0767b1 100644
--- a/src/gl/data/gl_setup.cpp
+++ b/src/gl/data/gl_setup.cpp
@@ -233,6 +233,7 @@ static void SpreadHackedFlag(subsector_t * sub)
 			if (!(sub2->hacked&1) && sub2->render_sector == sub->render_sector)
 			{
 				sub2->hacked|=1;
+				sub->hacked &= ~4;
 				SpreadHackedFlag (sub2);
 			}
 		}
@@ -285,7 +286,7 @@ static void PrepareSectorData()
 						subsectors[i].render_sector != seg[j].PartnerSeg->Subsector->render_sector)
 				{
 					DPrintf("Found hack: (%d,%d) (%d,%d)\n", seg[j].v1->x>>16, seg[j].v1->y>>16, seg[j].v2->x>>16, seg[j].v2->y>>16);
-					subsectors[i].hacked|=1;
+					subsectors[i].hacked|=5;
 					SpreadHackedFlag(&subsectors[i]);
 				}
 				if (seg[j].PartnerSeg==NULL) subsectors[i].hacked|=2;	// used for quick termination checks
diff --git a/src/gl/scene/gl_walls.cpp b/src/gl/scene/gl_walls.cpp
index bb160a790f..e86b03d490 100644
--- a/src/gl/scene/gl_walls.cpp
+++ b/src/gl/scene/gl_walls.cpp
@@ -1417,7 +1417,7 @@ void GLWall::Process(seg_t *seg, sector_t * frontsector, sector_t * backsector)
 	sector_t * realback;
 
 #ifdef _DEBUG
-	if (seg->linedef-lines==636)
+	if (seg->linedef-lines==1276)
 	{
 		int a = 0;
 	}
@@ -1635,7 +1635,11 @@ void GLWall::Process(seg_t *seg, sector_t * frontsector, sector_t * backsector)
 				}
 				else if (!(seg->sidedef->Flags & WALLF_POLYOBJ))
 				{
-					gl_drawinfo->AddUpperMissingTexture(seg->sidedef, sub, bch1a);
+					// skip processing if the back is a malformed subsector
+					if (!(seg->PartnerSeg->Subsector->hacked & 4))
+					{
+						gl_drawinfo->AddUpperMissingTexture(seg->sidedef, sub, bch1a);
+					}
 				}
 			}
 		}
@@ -1704,7 +1708,11 @@ void GLWall::Process(seg_t *seg, sector_t * frontsector, sector_t * backsector)
 			else if (backsector->GetTexture(sector_t::floor) != skyflatnum &&
 				!(seg->sidedef->Flags & WALLF_POLYOBJ))
 			{
-				gl_drawinfo->AddLowerMissingTexture(seg->sidedef, sub, bfh1);
+				// skip processing if the back is a malformed subsector
+				if (!(seg->PartnerSeg->Subsector->hacked & 4))
+				{
+					gl_drawinfo->AddLowerMissingTexture(seg->sidedef, sub, bfh1);
+				}
 			}
 		}
 	}