diff --git a/src/gl/models/gl_voxels.cpp b/src/gl/models/gl_voxels.cpp
index 288b1a9db6..6e84bd7abf 100644
--- a/src/gl/models/gl_voxels.cpp
+++ b/src/gl/models/gl_voxels.cpp
@@ -314,12 +314,12 @@ void FVoxelModel::MakeSlabPolys(int x, int y, kvxslab_t *voxptr, FVoxelMap &chec
 		}
 		if (cull & 4)
 		{
-			AddFace(x, y, z, x+1, y, z, x, y, z+c, x+1, y, z+c, *col, check);
+			AddFace(x+1, y, z, x, y, z, x+1, y, z+c, x, y, z+c, *col, check);
 		}
 		if (cull & 8)
 		{
-			AddFace(x+1, y+1, z, x, y+1, z, x+1, y+1, z+c, x, y+1, z+c, *col, check);
-		}
+			AddFace(x, y+1, z, x+1, y+1, z, x, y+1, z+c, x+1, y+1, z+c, *col, check);
+		}	
 		z+=c;
 		col+=c;
 	}
diff --git a/src/gl/scene/gl_flats.cpp b/src/gl/scene/gl_flats.cpp
index 394ca16265..c41e7664f9 100644
--- a/src/gl/scene/gl_flats.cpp
+++ b/src/gl/scene/gl_flats.cpp
@@ -187,21 +187,18 @@ void GLFlat::DrawSubsector(subsector_t * sub)
 		unsigned int vi[4];
 
 		vi[0] = 0;
-		for (unsigned int i = 1; i < sub->numlines-1; i += 2)
+		for (unsigned int i = 0; i < sub->numlines - 2; i += 2)
 		{
-			if (i < sub->numlines - 3)
+			for (unsigned int j = 1; j < 4; j++)
 			{
-				for (unsigned int j = 1; j < 4; j++)
-				{
-					vi[j] = MIN(i + j, sub->numlines - 1);
-				}
-				for (unsigned int x = 0; x < 4; x++)
-				{
-					vertex_t *vt = sub->firstline[vi[x]].v1;
-					qd.Set(x, vt->fX(), plane.plane.ZatPoint(vt) + dz, vt->fY(), vt->fX() / 64.f, -vt->fY() / 64.f);
-				}
-				qd.Render(GL_TRIANGLE_FAN);
+				vi[j] = MIN(i + j, sub->numlines - 1);
 			}
+			for (unsigned int x = 0; x < 4; x++)
+			{
+				vertex_t *vt = sub->firstline[vi[x]].v1;
+				qd.Set(x, vt->fX(), plane.plane.ZatPoint(vt) + dz, vt->fY(), vt->fX() / 64.f, -vt->fY() / 64.f);
+			}
+			qd.Render(GL_TRIANGLE_FAN);
 		}
 	}