diff --git a/src/p_enemy.c b/src/p_enemy.c
index 74a11fe67..774dddd3b 100644
--- a/src/p_enemy.c
+++ b/src/p_enemy.c
@@ -11559,10 +11559,7 @@ void A_BrakLobShot(mobj_t *actor)
 		return; // Don't even bother if we've got nothing to aim at.
 
 	// Look up actor's current gravity situation
-	if (actor->subsector->sector->gravity)
-		g = FixedMul(gravity,(FixedDiv(*actor->subsector->sector->gravity>>FRACBITS, 1000)));
-	else
-		g = gravity;
+	g = FixedMul(gravity, P_GetSectorGravity(actor->subsector->sector));
 
 	// Look up distance between actor and its target
 	x = P_AproxDistance(actor->target->x - actor->x, actor->target->y - actor->y);
@@ -11676,10 +11673,7 @@ void A_NapalmScatter(mobj_t *actor)
 		airtime = 16<<FRACBITS;
 
 	// Look up actor's current gravity situation
-	if (actor->subsector->sector->gravity)
-		g = FixedMul(gravity,(FixedDiv(*actor->subsector->sector->gravity>>FRACBITS, 1000)));
-	else
-		g = gravity;
+	g = FixedMul(gravity, P_GetSectorGravity(actor->subsector->sector));
 
 	// vy = (g*(airtime-1))/2
 	vy = FixedMul(g,(airtime-(1<<FRACBITS)))>>1;
@@ -12402,10 +12396,7 @@ void A_Boss5Jump(mobj_t *actor)
 		return; // Don't even bother if we've got nothing to aim at.
 
 	// Look up actor's current gravity situation
-	if (actor->subsector->sector->gravity)
-		g = FixedMul(gravity,(FixedDiv(*actor->subsector->sector->gravity>>FRACBITS, 1000)));
-	else
-		g = gravity;
+	g = FixedMul(gravity, P_GetSectorGravity(actor->subsector->sector));
 
 	// Look up distance between actor and its tracer
 	x = P_AproxDistance(actor->tracer->x - actor->x, actor->tracer->y - actor->y);
diff --git a/src/p_mobj.c b/src/p_mobj.c
index a2eaf7cf2..af349a8e0 100644
--- a/src/p_mobj.c
+++ b/src/p_mobj.c
@@ -1480,11 +1480,7 @@ fixed_t P_GetMobjGravity(mobj_t *mo)
 			if ((rover->flags & (FF_SWIMMABLE|FF_GOOWATER)) == (FF_SWIMMABLE|FF_GOOWATER))
 				goopgravity = true;
 
-			if (!(rover->master->frontsector->gravity))
-				continue;
-
-			gravityadd = -FixedMul(gravity,
-				(FixedDiv(*rover->master->frontsector->gravity>>FRACBITS, 1000)));
+			gravityadd = -FixedMul(gravity, P_GetSectorGravity(rover->master->frontsector));
 
 			if (rover->master->frontsector->verticalflip && gravityadd > 0)
 				mo->eflags |= MFE_VERTICALFLIP;
@@ -1496,11 +1492,7 @@ fixed_t P_GetMobjGravity(mobj_t *mo)
 
 	if (no3dfloorgrav)
 	{
-		if (mo->subsector->sector->gravity)
-			gravityadd = -FixedMul(gravity,
-				(FixedDiv(*mo->subsector->sector->gravity>>FRACBITS, 1000)));
-		else
-			gravityadd = -gravity;
+		gravityadd = -FixedMul(gravity, P_GetSectorGravity(mo->subsector->sector));
 
 		if (mo->subsector->sector->verticalflip && gravityadd > 0)
 			mo->eflags |= MFE_VERTICALFLIP;
diff --git a/src/p_setup.c b/src/p_setup.c
index a613835c8..bd3d03e1b 100644
--- a/src/p_setup.c
+++ b/src/p_setup.c
@@ -831,8 +831,8 @@ static void GeneralDefaults(void)
 		// Defaults.
 		sc->floor_xoffs = sc->ceiling_xoffs = sc->floor_yoffs = sc->ceiling_yoffs = 0;
 		sc->floorpic_angle = sc->ceilingpic_angle = 0;
-		//sc->gravity = FRACUNIT;
-		sc->gravity = NULL;
+		sc->gravity = FRACUNIT;
+		sc->gravityptr = NULL;
 		sc->verticalflip = false;
 //		sc->udmfflags = 0;
 
@@ -930,7 +930,7 @@ static void TextmapDefaults (void)
 		sc->floor_xoffs = sc->floor_yoffs = sc->ceiling_xoffs = sc->ceiling_yoffs = 0;
 		sc->floorpic_angle = sc->ceilingpic_angle = 0;
 
-//		sc->gravity = FRACUNIT;
+		sc->gravity = FRACUNIT;
 		sc->verticalflip = false;
 //		sc->udmfflags = 0;
 
@@ -1064,11 +1064,11 @@ static void TextmapSector(UINT32 i, char *param)
 		sectors[i].floorpic_angle = FixedAngle(FLOAT_TO_FIXED(atof(M_GetToken(NULL))));
 	else if (fastcmp(param, "rotationceiling"))
 		sectors[i].ceilingpic_angle = FixedAngle(FLOAT_TO_FIXED(atof(M_GetToken(NULL))));
-	#ifdef ADVUDMF
 	else if (fastcmp(param, "gravity"))
 		sectors[i].gravity = FLOAT_TO_FIXED(atof(M_GetToken(NULL)));
 	else if (fastcmp(param, "flip") && fastcmp("true", M_GetToken(NULL)))
 		sectors[i].verticalflip = true;
+	#ifdef ADVUDMF
 	else if (fastcmp(param, "heatwave") && fastcmp("true", M_GetToken(NULL)))
 		sectors[i].udmfflags |= SFU_HEATWAVE;
 	#endif
diff --git a/src/p_spec.c b/src/p_spec.c
index 323321016..4bb5bc25b 100644
--- a/src/p_spec.c
+++ b/src/p_spec.c
@@ -975,6 +975,15 @@ static sector_t *P_FindModelCeilingSector(fixed_t ceildestheight, INT32 secnum)
 }
 #endif
 
+// Calculates the per-sector gravity.
+fixed_t P_GetSectorGravity(sector_t *sec)
+{
+	if (sec->gravityptr)
+		return FixedDiv(*sec->gravityptr >> FRACBITS, 1000);
+	else
+		return sec->gravity;
+}
+
 /** Searches the tag lists for the next sector tagged to a line.
   *
   * \param line  Tagged line used as a reference.
@@ -6576,6 +6585,9 @@ void P_SpawnSpecials(INT32 fromnetsave)
 	sector = sectors;
 	for (i = 0; i < numsectors; i++, sector++)
 	{
+		if (sector->verticalflip)
+			CheckForReverseGravity = true;
+
 		if (!sector->special)
 			continue;
 
@@ -6691,12 +6703,11 @@ void P_SpawnSpecials(INT32 fromnetsave)
 			INT32 s;
 			size_t sec;
 			ffloortype_e ffloorflags;
-
 			case 1: // Definable gravity per sector
 				sec = sides[*lines[i].sidenum].sector - sectors;
 				for (s = -1; (s = P_FindSectorFromLineTag(lines + i, s)) >= 0 ;)
 				{
-					sectors[s].gravity = &sectors[sec].floorheight; // This allows it to change in realtime!
+					sectors[s].gravityptr = &sectors[sec].floorheight; // This allows it to change in realtime!
 
 					if (lines[i].flags & ML_NOCLIMB)
 						sectors[s].verticalflip = true;
diff --git a/src/p_spec.h b/src/p_spec.h
index dcf03cbd1..6788353bf 100644
--- a/src/p_spec.h
+++ b/src/p_spec.h
@@ -53,6 +53,8 @@ fixed_t P_FindNextLowestFloor(sector_t *sec, fixed_t currentheight);
 fixed_t P_FindLowestCeilingSurrounding(sector_t *sec);
 fixed_t P_FindHighestCeilingSurrounding(sector_t *sec);
 
+fixed_t P_GetSectorGravity(sector_t *sec);
+
 INT32 P_FindSectorFromLineTag(line_t *line, INT32 start);
 INT32 P_FindSectorFromTag(INT16 tag, INT32 start);
 INT32 P_FindSpecialLineFromTag(INT16 special, INT16 tag, INT32 start);
diff --git a/src/r_defs.h b/src/r_defs.h
index c0116fbc8..3d1f80a3c 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -372,7 +372,7 @@ typedef struct sector_s
 #endif // ----- end special tricks -----
 
 	// This points to the master's floorheight, so it can be changed in realtime!
-	fixed_t *gravity; // per-sector gravity
+	fixed_t gravity; // per-sector gravity
 	fixed_t *gravityptr; // For binary format: Read gravity from floor height of master sector
 	boolean verticalflip; // If gravity < 0, then allow flipped physics
 	sectorflags_t flags;