diff --git a/source/build/src/clip.cpp b/source/build/src/clip.cpp
index 4bb6481f3..10848d3ab 100644
--- a/source/build/src/clip.cpp
+++ b/source/build/src/clip.cpp
@@ -120,61 +120,8 @@ inline void clipmove_tweak_pos(const vec3_t *pos, int32_t gx, int32_t gy, int32_
 static int cliptestsector(int const dasect, int const nextsect, int32_t const flordist, int32_t const ceildist, vec2_t const pos, int32_t const posz)
 {
 	assert(validSectorIndex(dasect) && validSectorIndex(nextsect));
-
-    auto const sec2 = &sector[nextsect];
-
-    switch (enginecompatibility_mode)
-    {
-    case ENGINECOMPATIBILITY_NONE:
-        break;
-    default:
-    {
-        int32_t daz = int_getflorzofslopeptr(&sector[dasect], pos.X, pos.Y);
-        int32_t daz2 = int_getflorzofslopeptr(sec2, pos.X, pos.Y);
-
-        if (daz2 < daz-(1<<8) && (sec2->floorstat & CSTAT_SECTOR_SKY) == 0)
-            if (posz >= daz2-(flordist-1)) return 1;
-        daz = int_getceilzofslopeptr(&sector[dasect], pos.X, pos.Y);
-        daz2 = int_getceilzofslopeptr(sec2, pos.X, pos.Y);
-        if (daz2 > daz+(1<<8) && (sec2->ceilingstat & CSTAT_SECTOR_SKY) == 0)
-            if (posz <= daz2+(ceildist-1)) return 1;
-
-        return 0;
-    }
-    }
-
-    double daz2  = sec2->floorz;
-    double dacz2 = sec2->ceilingz;
-
-    if ((sec2->floorstat|sec2->ceilingstat) & CSTAT_SECTOR_SLOPE)
-        getcorrectzsofslope(nextsect, pos.X, pos.Y, &dacz2, &daz2);
-
-    if (daz2 <= dacz2)
-        return 1;
-
-    auto const sec = &sector[dasect];
-
-    double daz  = sec->floorz;
-    double dacz = sec->ceilingz;
-
-    if ((sec->floorstat|sec->ceilingstat) & CSTAT_SECTOR_SLOPE)
-        getcorrectzsofslope(dasect, pos.X, pos.Y, &dacz, &daz);
-
-    double const sec2height = abs(daz2-dacz2);
-    double fposz = posz * zinttoworld;
-    double fceildist = ceildist * zinttoworld;
-    double fflordist = flordist * zinttoworld;
-
-    return ((abs(daz-dacz) > sec2height &&       // clip if the current sector is taller and the next is too small
-            sec2height < (fceildist + (CLIPCURBHEIGHT * 2))) ||
-
-            ((sec2->floorstat & CSTAT_SECTOR_SKY) == 0 &&    // parallaxed floor curbs don't clip
-            fposz >= daz2-(fflordist-1) &&    // also account for desired z distance tolerance
-            daz2 < daz-CLIPCURBHEIGHT) ||   // curbs less tall than 256 z units don't clip
-
-            ((sec2->ceilingstat & CSTAT_SECTOR_SKY) == 0 && 
-            fposz <= dacz2+(fceildist-1) &&
-            dacz2 > dacz+CLIPCURBHEIGHT));  // ceilings check the same conditions ^^^^^
+    return checkOpening(DVector2(pos.X * inttoworld, pos.Y * inttoworld), posz * zinttoworld, &sector[dasect], &sector[nextsect], 
+        ceildist * zinttoworld, flordist * zinttoworld, enginecompatibility_mode == ENGINECOMPATIBILITY_NONE);
 }
 
 //
diff --git a/source/core/gamefuncs.cpp b/source/core/gamefuncs.cpp
index a96d8fcde..e963bb57b 100644
--- a/source/core/gamefuncs.cpp
+++ b/source/core/gamefuncs.cpp
@@ -150,17 +150,6 @@ void calcSlope(const sectortype* sec, double xpos, double ypos, double* pceilz,
 	}
 }
 
-// only used by clipmove et.al.
-void getcorrectzsofslope(int sectnum, int dax, int day, double* ceilz, double* florz)
-{
-	DVector2 closestv;
-	SquareDistToSector(dax * inttoworld, day * inttoworld, &sector[sectnum], &closestv);
-	double ffloorz, fceilz;
-	calcSlope(&sector[sectnum], closestv.X, closestv.Y, &fceilz, &ffloorz);
-	if (ceilz) *ceilz = fceilz;
-	if (florz) *florz = ffloorz;
-}
-
 //==========================================================================
 //
 // 
@@ -1193,6 +1182,13 @@ bool checkOpening(const DVector2& inpos, double z, const sectortype* sec, const
 	calcSlope(sec, pos.X, pos.Y, &c1, &f1);
 	calcSlope(nextsec, pos.X, pos.Y, &c2, &f2);
 
+	if (precise)
+	{
+		double sech = abs(f1 - c1);
+		double nextsech = abs(f2 - c2);
+		if (sech > nextsech && nextsech < ceilingdist + 2) return 1;
+	}
+
 	return ((f2 < f1 - 1 && (nextsec->floorstat & CSTAT_SECTOR_SKY) == 0 && z >= f2 - (floordist - zmaptoworld)) ||
 		(c2 > c1 + 1 && (nextsec->ceilingstat & CSTAT_SECTOR_SKY) == 0 && z <= c2 + (ceilingdist - zmaptoworld)));
 }