diff --git a/src/hardware/hw_main.c b/src/hardware/hw_main.c
index f533082f7..68681295e 100644
--- a/src/hardware/hw_main.c
+++ b/src/hardware/hw_main.c
@@ -1533,14 +1533,14 @@ static void HWR_ProcessSeg(void)
 				if ((high1 < lowcut && highslope1 < lowcutslope) || (low1 > highcut && lowslope1 > highcutslope))
 					continue;
 
-				side_t *side = R_GetFFloorSide(gl_curline, rover);
+				side_t *side = R_GetFFloorSide(gl_curline->linedef, rover, gl_backsector);
 
 				boolean do_texture_skew;
 				boolean dont_peg_bottom;
 
 				if (rover->master->flags & ML_TFERLINE)
 				{
-					line_t *newline = R_GetFFloorLine(gl_curline, rover);
+					line_t *newline = R_GetFFloorLine(gl_curline->linedef, rover, gl_backsector);
 					do_texture_skew = newline->flags & ML_SKEWTD;
 					dont_peg_bottom = newline->flags & ML_DONTPEGBOTTOM;
 				}
@@ -1689,14 +1689,14 @@ static void HWR_ProcessSeg(void)
 				if ((high1 < lowcut && highslope1 < lowcutslope) || (low1 > highcut && lowslope1 > highcutslope))
 					continue;
 
-				side_t *side = R_GetFFloorSide(gl_curline, rover);
+				side_t *side = R_GetFFloorSide(gl_curline->linedef, rover, gl_backsector);
 
 				boolean do_texture_skew;
 				boolean dont_peg_bottom;
 
 				if (rover->master->flags & ML_TFERLINE)
 				{
-					line_t *newline = R_GetFFloorLine(gl_curline, rover);
+					line_t *newline = R_GetFFloorLine(gl_curline->linedef, rover, gl_backsector);
 					do_texture_skew = newline->flags & ML_SKEWTD;
 					dont_peg_bottom = newline->flags & ML_DONTPEGBOTTOM;
 				}
diff --git a/src/r_main.c b/src/r_main.c
index 462439294..067b8abdb 100644
--- a/src/r_main.c
+++ b/src/r_main.c
@@ -390,22 +390,22 @@ fixed_t R_PointToDist(fixed_t x, fixed_t y)
 	return R_PointToDist2(viewx, viewy, x, y);
 }
 
-line_t *R_GetFFloorLine(const seg_t *seg, const ffloor_t *pfloor)
+line_t *R_GetFFloorLine(const line_t *line, const ffloor_t *pfloor, const sector_t *sector)
 {
 	if (pfloor->master->flags & ML_TFERLINE)
 	{
-		size_t linenum = seg->linedef - pfloor->target->lines[0];
+		size_t linenum = min((size_t)(line - sector->lines[0]), pfloor->master->frontsector->linecount);
 		return pfloor->master->frontsector->lines[0] + linenum;
 	}
 	else
 		return pfloor->master;
 }
 
-side_t *R_GetFFloorSide(const seg_t *seg, const ffloor_t *pfloor)
+side_t *R_GetFFloorSide(const line_t *line, const ffloor_t *pfloor, const sector_t *sector)
 {
 	if (pfloor->master->flags & ML_TFERLINE)
 	{
-		line_t *newline = R_GetFFloorLine(seg, pfloor);
+		line_t *newline = R_GetFFloorLine(line, pfloor, sector);
 		return &sides[newline->sidenum[0]];
 	}
 	else
diff --git a/src/r_main.h b/src/r_main.h
index aedfeb6ad..64a69fffe 100644
--- a/src/r_main.h
+++ b/src/r_main.h
@@ -86,8 +86,8 @@ subsector_t *R_PointInSubsectorOrNull(fixed_t x, fixed_t y);
 
 boolean R_DoCulling(line_t *cullheight, line_t *viewcullheight, fixed_t vz, fixed_t bottomh, fixed_t toph);
 
-line_t *R_GetFFloorLine(const seg_t *seg, const ffloor_t *pfloor);
-side_t *R_GetFFloorSide(const seg_t *seg, const ffloor_t *pfloor);
+line_t *R_GetFFloorLine(const line_t *line, const ffloor_t *pfloor, const sector_t *sector);
+side_t *R_GetFFloorSide(const line_t *line, const ffloor_t *pfloor, const sector_t *sector);
 
 // Render stats
 
diff --git a/src/r_segs.c b/src/r_segs.c
index d7296583c..19fdcfca7 100644
--- a/src/r_segs.c
+++ b/src/r_segs.c
@@ -574,13 +574,13 @@ void R_RenderThickSideRange(drawseg_t *ds, INT32 x1, INT32 x2, ffloor_t *pfloor)
 	curline = ds->curline;
 	backsector = pfloor->target;
 	frontsector = curline->frontsector == pfloor->target ? curline->backsector : curline->frontsector;
-	sidedef = R_GetFFloorSide(curline, pfloor);
+	sidedef = R_GetFFloorSide(curline->linedef, pfloor, pfloor->target);
 
 	colfunc = colfuncs[BASEDRAWFUNC];
 
 	if (pfloor->master->flags & ML_TFERLINE)
 	{
-		line_t *newline = R_GetFFloorLine(curline, pfloor);
+		line_t *newline = R_GetFFloorLine(curline->linedef, pfloor, pfloor->target);
 		do_texture_skew = newline->flags & ML_SKEWTD;
 		dont_peg_bottom = newline->flags & ML_DONTPEGBOTTOM;
 	}