diff --git a/am_main.c b/am_main.c
index 6e5d145f3..de5baa0b7 100644
--- a/am_main.c
+++ b/am_main.c
@@ -655,10 +655,12 @@ static void AM_Drawer_ (int c)
 	for (i=0 ; i<numlines ; i++,line++)
 	{
 		int flags;
+		int mapped;
 		mapvertex_t *v1, *v2;
 
 		flags = line->flags;
-		if ((!(flags & ML_MAPPED) ||		/* IF NOT MAPPED OR DON'T DRAW */
+		mapped = LD_MAPPED(line);
+		if ((!mapped ||		/* IF NOT MAPPED OR DON'T DRAW */
 			flags & ML_DONTDRAW) &&
 			(!(p->powers[pw_allmap] + showAllLines)))
 			continue;
@@ -708,7 +710,7 @@ static void AM_Drawer_ (int c)
 		color = CRY_BROWN;
 		if ((p->powers[pw_allmap] +
 			showAllLines) &&			/* IF COMPMAP && !MAPPED YET */
-			!(flags & ML_MAPPED))
+			!mapped)
 			color = CRY_GREY;
 		else
 		if (!(flags & ML_TWOSIDED))	/* ONE-SIDED LINE */
diff --git a/doomdata.h b/doomdata.h
index 7134d6735..b70483d01 100644
--- a/doomdata.h
+++ b/doomdata.h
@@ -62,15 +62,8 @@ typedef struct
 #define ML_SECRET			32	/* don't map as two sided: IT'S A SECRET! */
 #define ML_SOUNDBLOCK		64	/* don't let sound cross two of these */
 #define	ML_DONTDRAW			128	/* don't draw on the automap */
-#define	ML_MAPPED			256	/* set if allready drawn in automap */
 
 
-/* to aid move clipping */
-#define ML_ST_HORIZONTAL 	512
-#define ML_ST_VERTICAL	 	1024
-#define ML_ST_POSITIVE	 	2048
-#define ML_ST_NEGATIVE	 	4096
-
 typedef	struct
 {
 	short		floorheight, ceilingheight;
diff --git a/p_maputl.c b/p_maputl.c
index 61b724cec..88e69c1dc 100644
--- a/p_maputl.c
+++ b/p_maputl.c
@@ -88,7 +88,7 @@ boolean P_BoxCrossLine(line_t *ld, fixed_t testbbox[4])
       return false;
    }
 
-   if(ld->flags & ML_ST_POSITIVE)
+   if(LD_SLOPE_POSITIVE(ld))
    {
       x1 = testbbox[BOXLEFT ];
       x2 = testbbox[BOXRIGHT];
diff --git a/p_setup.c b/p_setup.c
index 5e6c74c6f..260bf4baa 100644
--- a/p_setup.c
+++ b/p_setup.c
@@ -117,7 +117,7 @@ void P_LoadSegs (int lump)
 		li->sideoffset |= side;
 
 		if (ldef->v1 == li->v1)
-			ldef->fineangle = angle >> ANGLETOFINESHIFT;
+			ldef->fineangle |= (angle >> ANGLETOFINESHIFT);
 	}
 }
 
@@ -449,16 +449,10 @@ void P_LoadLineDefs (int lump)
 		v2 = &vertexes[ld->v2];
 		dx = (v2->x - v1->x) << FRACBITS;
 		dy = (v2->y - v1->y) << FRACBITS;
-		if (!dx)
-			ld->flags |= ML_ST_VERTICAL;
-		else if (!dy)
-			ld->flags |= ML_ST_HORIZONTAL;
-		else
+		if (dx && dy)
 		{
 			if (FixedDiv (dy , dx) > 0)
-				ld->flags |= ML_ST_POSITIVE;
-			else
-				ld->flags |= ML_ST_NEGATIVE;
+				ld->fineangle |= 0x8000;
 		}
 
 		ld->sidenum[0] = LITTLESHORT(mld->sidenum[0]);
diff --git a/p_slide.c b/p_slide.c
index ebe4e6f74..0fc91824f 100644
--- a/p_slide.c
+++ b/p_slide.c
@@ -162,6 +162,7 @@ static boolean SL_CheckLine(line_t *ld, pslidework_t *sw)
    fixed_t   opentop, openbottom;
    sector_t *front, *back;
    int       side1;
+   int      fineangle;
    vertex_t vtmp;
    fixed_t  ldbbox[4];
 
@@ -201,12 +202,13 @@ static boolean SL_CheckLine(line_t *ld, pslidework_t *sw)
 
    // the line is definitely blocking movement at this point
 findfrac:
+   fineangle = LD_FINEANGLE(ld);
    sw->p1.x = vertexes[ld->v1].x << FRACBITS;
    sw->p1.y = vertexes[ld->v1].y << FRACBITS;
    sw->p2.x = vertexes[ld->v2].x << FRACBITS;
    sw->p2.y = vertexes[ld->v2].y << FRACBITS;
-   sw->nvx = finesine(ld->fineangle);
-   sw->nvy = -finecosine(ld->fineangle);
+   sw->nvx = finesine(fineangle);
+   sw->nvy = -finecosine(fineangle);
    
    side1 = SL_PointOnSide(sw, sw->slidex, sw->slidey);
    switch(side1)
diff --git a/r_local.h b/r_local.h
index 8f9e48af9..8812eea45 100644
--- a/r_local.h
+++ b/r_local.h
@@ -109,16 +109,24 @@ typedef struct
 
 typedef struct line_s
 {
-	VINT		flags;
 	VINT		sidenum[2];			/* sidenum[1] will be -1 if one sided */
 	VINT 		v1, v2;
-	VINT		special, tag;
+	uint8_t		flags, special;
+	VINT		tag;
 	VINT		fineangle;			/* to get sine / eosine for sliding */
+									/* bit 15 is set if the slope is positive */
+									/* bit 14 is set if allready drawn in automap */
 } line_t;
 
 #define LD_FRONTSECTOR(ld) (&sectors[sides[(ld)->sidenum[0]].sector])
 #define LD_BACKSECTOR(ld) ((ld)->sidenum[1] != -1 ? &sectors[sides[ld->sidenum[1]].sector] : NULL)
 
+#define LD_SEEN 0x4000
+
+#define LD_MAPPED(ld) ((ld->fineangle & LD_SEEN) != 0)
+#define LD_SLOPE_POSITIVE(ld) (ld->fineangle < 0 ? true : false)
+#define LD_FINEANGLE(ld) (ld->fineangle & FINEMASK)
+
 typedef struct subsector_s
 {
 	VINT		numlines;
diff --git a/r_phase1.c b/r_phase1.c
index 7339d6c24..51f1e9ce2 100644
--- a/r_phase1.c
+++ b/r_phase1.c
@@ -198,7 +198,7 @@ static void R_WallEarlyPrep(viswall_t* segl, fixed_t *restrict floorheight,
    const short liflags = li->flags;
 
    {
-      li->flags |= ML_MAPPED; // mark as seen
+      li->fineangle |= LD_SEEN; // mark as seen
 
       textureoffset = si->textureoffset & 0xfff;
       textureoffset <<= 4; // sign extend