diff --git a/src/am_map.cpp b/src/am_map.cpp
index 81e45c685..606a65ae8 100644
--- a/src/am_map.cpp
+++ b/src/am_map.cpp
@@ -2071,17 +2071,17 @@ static bool AM_CheckSecret(line_t *line)
 	{
 		if (line->frontsector != NULL)
 		{
-			if (line->frontsector->secretsector)
+			if (line->frontsector->wasSecret())
 			{
-				if (am_map_secrets!=0 && !(line->frontsector->special&SECRET_MASK)) return true;
+				if (am_map_secrets!=0 && !line->frontsector->isSecret()) return true;
 				if (am_map_secrets==2 && !(line->flags & ML_SECRET)) return true;
 			}
 		}
 		if (line->backsector != NULL)
 		{
-			if (line->backsector->secretsector)
+			if (line->backsector->wasSecret())
 			{
-				if (am_map_secrets!=0 && !(line->backsector->special&SECRET_MASK)) return true;
+				if (am_map_secrets!=0 && !line->backsector->isSecret()) return true;
 				if (am_map_secrets==2 && !(line->flags & ML_SECRET)) return true;
 			}
 		}
diff --git a/src/c_cmds.cpp b/src/c_cmds.cpp
index 0a9e4f0e3..57290a98a 100644
--- a/src/c_cmds.cpp
+++ b/src/c_cmds.cpp
@@ -1106,11 +1106,8 @@ static void PrintSecretString(const char *string, bool thislevel)
 				if (*string == ';') string++;
 				if (thislevel && secnum >= 0 && secnum < numsectors)
 				{
-					if (sectors[secnum].secretsector)
-					{
-						if ((sectors[secnum].special & SECRET_MASK)) colstr = TEXTCOLOR_RED;
-						else colstr = TEXTCOLOR_GREEN;
-					}
+					if (sectors[secnum].isSecret()) colstr = TEXTCOLOR_RED;
+					else if (sectors[secnum].wasSecret()) colstr = TEXTCOLOR_GREEN;
 					else colstr = TEXTCOLOR_ORANGE;
 				}
 			}
diff --git a/src/g_strife/a_strifestuff.cpp b/src/g_strife/a_strifestuff.cpp
index 1edea19fa..7e9330990 100644
--- a/src/g_strife/a_strifestuff.cpp
+++ b/src/g_strife/a_strifestuff.cpp
@@ -632,7 +632,7 @@ DEFINE_ACTION_FUNCTION(AActor, A_CheckTerrain)
 	{
 		if ((sec->special & 0xFF) == Damage_InstantDeath)
 		{
-			P_DamageMobj (self, NULL, NULL, 999, NAME_None);
+			P_DamageMobj (self, NULL, NULL, 999, NAME_InstantDeath);
 		}
 		else if ((sec->special & 0xFF) == Scroll_StrifeCurrent)
 		{
diff --git a/src/p_3dfloors.cpp b/src/p_3dfloors.cpp
index 6af26652f..3fbbfeab7 100644
--- a/src/p_3dfloors.cpp
+++ b/src/p_3dfloors.cpp
@@ -342,8 +342,7 @@ void P_PlayerOnSpecial3DFloor(player_t* player)
 		}
 
 		// Apply sector specials
-		if (rover->model->special || rover->model->damageamount)
-			P_PlayerInSpecialSector(player, rover->model);
+		P_PlayerInSpecialSector(player, rover->model);
 
 		// Apply flat specials (using the ceiling!)
 		P_PlayerOnSpecialFlat(
diff --git a/src/p_floor.cpp b/src/p_floor.cpp
index 9e7806039..42372888b 100644
--- a/src/p_floor.cpp
+++ b/src/p_floor.cpp
@@ -159,7 +159,7 @@ void DFloor::Tick ()
 				case donutRaise:
 				case genFloorChgT:
 				case genFloorChg0:
-					m_Sector->special = (m_Sector->special & SECRET_MASK) | m_NewSpecial;
+					m_Sector->special = m_Sector->special | m_NewSpecial;
 					//fall thru
 				case genFloorChg:
 					m_Sector->SetTexture(sector_t::floor, m_Texture);
@@ -175,7 +175,7 @@ void DFloor::Tick ()
 				case floorLowerAndChange:
 				case genFloorChgT:
 				case genFloorChg0:
-					m_Sector->special = (m_Sector->special & SECRET_MASK) | m_NewSpecial;
+					m_Sector->special = m_Sector->special | m_NewSpecial;
 					//fall thru
 				case genFloorChg:
 					m_Sector->SetTexture(sector_t::floor, m_Texture);
@@ -240,7 +240,7 @@ void DFloor::SetFloorChangeType (sector_t *sec, int change)
 		m_Type = DFloor::genFloorChg;
 		break;
 	case 3:
-		m_NewSpecial = sec->special & ~SECRET_MASK;
+		m_NewSpecial = sec->special;
 		m_Type = DFloor::genFloorChgT;
 		break;
 	}
@@ -438,11 +438,11 @@ bool EV_DoFloor (DFloor::EFloor floortype, line_t *line, int tag,
 			{
 				FTextureID oldpic = sec->GetTexture(sector_t::floor);
 				sec->SetTexture(sector_t::floor, line->frontsector->GetTexture(sector_t::floor));
-				sec->special = (sec->special & SECRET_MASK) | (line->frontsector->special & ~SECRET_MASK);
+				sec->special = line->frontsector->special;
 			}
 			else
 			{
-				sec->special &= SECRET_MASK;
+				sec->special = 0;
 			}
 			break;
 		  
@@ -454,7 +454,7 @@ bool EV_DoFloor (DFloor::EFloor floortype, line_t *line, int tag,
 			// jff 1/24/98 make sure floor->m_NewSpecial gets initialized
 			// in case no surrounding sector is at floordestheight
 			// --> should not affect compatibility <--
-			floor->m_NewSpecial = sec->special & ~SECRET_MASK; 
+			floor->m_NewSpecial = sec->special; 
 
 			//jff 5/23/98 use model subroutine to unify fixes and handling
 			sector_t *modelsec;
@@ -462,7 +462,7 @@ bool EV_DoFloor (DFloor::EFloor floortype, line_t *line, int tag,
 			if (modelsec != NULL)
 			{
 				floor->m_Texture = modelsec->GetTexture(sector_t::floor);
-				floor->m_NewSpecial = modelsec->special & ~SECRET_MASK;
+				floor->m_NewSpecial = modelsec->special;
 			}
 			break;
 
@@ -1091,7 +1091,7 @@ bool EV_DoChange (line_t *line, EChange changetype, int tag)
 			if (line)
 			{ // [RH] if no line, no change
 				sec->SetTexture(sector_t::floor, line->frontsector->GetTexture(sector_t::floor));
-				sec->special = (sec->special & SECRET_MASK) | (line->frontsector->special & ~SECRET_MASK);
+				sec->special = line->frontsector->special;
 			}
 			break;
 		case numChangeOnly:
diff --git a/src/p_lnspec.cpp b/src/p_lnspec.cpp
index 8fa8691b2..53090ef18 100644
--- a/src/p_lnspec.cpp
+++ b/src/p_lnspec.cpp
@@ -1945,6 +1945,9 @@ FUNC(LS_Sector_ChangeFlags)
 
 	rtn = false;
 	FSectorTagIterator itr(arg0);
+	// exclude protected flags
+	arg1 &= ~SECF_NOMODIFY;
+	arg2 &= ~SECF_NOMODIFY;
 	while ((secNum = itr.Next()) >= 0)
 	{
 		sectors[secNum].Flags = (sectors[secNum].Flags | arg1) & ~arg2;
diff --git a/src/p_lnspec.h b/src/p_lnspec.h
index 9fb4c17b3..cb3f6bf85 100644
--- a/src/p_lnspec.h
+++ b/src/p_lnspec.h
@@ -176,10 +176,12 @@ typedef enum {
 
 // [RH] Equivalents for BOOM's generalized sector types
 
+#ifndef SECRET_MASK
 #define DAMAGE_MASK		0x0300
 #define SECRET_MASK		0x0400
 #define FRICTION_MASK	0x0800
 #define PUSH_MASK		0x1000
+#endif
 
 struct line_t;
 class AActor;
diff --git a/src/p_plats.cpp b/src/p_plats.cpp
index 7600637b2..eecf521ee 100644
--- a/src/p_plats.cpp
+++ b/src/p_plats.cpp
@@ -281,7 +281,7 @@ bool EV_DoPlat (int tag, line_t *line, DPlat::EPlatType type, int height,
 			if (line)
 				sec->SetTexture(sector_t::floor, line->sidedef[0]->sector->GetTexture(sector_t::floor));
 			if (change == 1)
-				sec->special &= SECRET_MASK;	// Stop damage and other stuff, if any
+				sec->special = 0;	// Stop damage and other stuff, if any
 		}
 
 		switch (type)
@@ -293,7 +293,7 @@ bool EV_DoPlat (int tag, line_t *line, DPlat::EPlatType type, int height,
 			plat->m_Low = sec->floorplane.d;
 			plat->m_Status = DPlat::up;
 			plat->PlayPlatSound ("Floor");
-			sec->special &= SECRET_MASK;		// NO MORE DAMAGE, IF APPLICABLE
+			sec->special = 0;		// NO MORE DAMAGE, IF APPLICABLE
 			break;
 
 		case DPlat::platUpByValue:
diff --git a/src/p_saveg.cpp b/src/p_saveg.cpp
index fdf57ddb0..fa1f395cf 100644
--- a/src/p_saveg.cpp
+++ b/src/p_saveg.cpp
@@ -398,15 +398,25 @@ void P_SerializeWorld (FArchive &arc)
 			}
 		}
 
-		arc	<< sec->SoundTarget
+		arc << sec->SoundTarget
 			<< sec->SecActTarget
 			<< sec->sky
 			<< sec->MoreFlags
 			<< sec->Flags
 			<< sec->FloorSkyBox << sec->CeilingSkyBox
-			<< sec->ZoneNumber
-			<< sec->secretsector
-			<< sec->interpolations[0]
+			<< sec->ZoneNumber;
+		if (SaveVersion < 4529)
+		{
+			short secretsector;
+			arc << secretsector;
+			if (secretsector) sec->Flags |= SECF_WASSECRET;
+			if (sec->special & SECRET_MASK)
+			{
+				sec->Flags |= SECF_SECRET;
+				sec->special &= ~SECRET_MASK;
+			}
+		}
+		arc	<< sec->interpolations[0]
 			<< sec->interpolations[1]
 			<< sec->interpolations[2]
 			<< sec->interpolations[3]
diff --git a/src/p_setup.cpp b/src/p_setup.cpp
index 50e7f41d6..dbd0954cc 100644
--- a/src/p_setup.cpp
+++ b/src/p_setup.cpp
@@ -1512,7 +1512,6 @@ void P_LoadSectors (MapData *map, FMissingTextureTracker &missingtex)
 			ss->special = LittleShort(ms->special);
 		else	// [RH] Translate to new sector special
 			ss->special = P_TranslateSectorSpecial (LittleShort(ms->special));
-		ss->secretsector = !!(ss->special&SECRET_MASK);
 		tagManager.AddSectorTag(i, LittleShort(ms->tag));
 		ss->thinglist = NULL;
 		ss->touching_thinglist = NULL;		// phares 3/14/98
diff --git a/src/p_spec.cpp b/src/p_spec.cpp
index c439ac50e..d94d91ac5 100644
--- a/src/p_spec.cpp
+++ b/src/p_spec.cpp
@@ -437,7 +437,7 @@ void P_PlayerInSpecialSector (player_t *player, sector_t * sector)
 		}
 	}
 
-	int special = sector->special & ~SECRET_MASK;
+	int special = sector->special;
 
 	// Has hit ground.
 	AInventory *ironfeet;
@@ -574,9 +574,9 @@ void P_PlayerInSpecialSector (player_t *player, sector_t * sector)
 		}
 	}
 
-	if (sector->special & SECRET_MASK)
+	if (sector->isSecret())
 	{
-		sector->special &= ~SECRET_MASK;
+		sector->ClearSecret();
 		P_GiveSecret(player->mo, true, true, int(sector - sectors));
 	}
 }
@@ -1189,7 +1189,11 @@ void P_SpawnSpecials (void)
 
 		// [RH] All secret sectors are marked with a BOOM-ish bitfield
 		if (sector->special & SECRET_MASK)
+		{
+			sector->Flags |= SECF_SECRET | SECF_WASSECRET;
+			sector->special &= ~SECRET_MASK;
 			level.total_secrets++;
+		}
 
 		switch (sector->special & 0xff)
 		{
diff --git a/src/p_udmf.cpp b/src/p_udmf.cpp
index 2169da49f..128225e4a 100644
--- a/src/p_udmf.cpp
+++ b/src/p_udmf.cpp
@@ -1567,8 +1567,6 @@ public:
 				if (sc.Number != 0)	tagManager.AddSectorTag(index, sc.Number);
 			}
 		}
-
-		sec->secretsector = !!(sec->special&SECRET_MASK);
 		
 		// Reset the planes to their defaults if not all of the plane equation's parameters were found.
 		if (fplaneflags != 15)
diff --git a/src/p_user.cpp b/src/p_user.cpp
index 8f8a93fdb..922cc2a1c 100644
--- a/src/p_user.cpp
+++ b/src/p_user.cpp
@@ -2538,10 +2538,8 @@ void P_PlayerThink (player_t *player)
 	if (!(player->cheats & CF_PREDICTING))
 	{
 		P_PlayerOnSpecial3DFloor (player);
-		if (player->mo->Sector->special || player->mo->Sector->damageamount != 0)
-		{
-			P_PlayerInSpecialSector (player);
-		}
+		P_PlayerInSpecialSector (player);
+
 		if (player->mo->z <= player->mo->Sector->floorplane.ZatPoint(
 			player->mo->x, player->mo->y) ||
 			player->mo->waterlevel)
diff --git a/src/r_defs.h b/src/r_defs.h
index 89449f446..0c873beeb 100644
--- a/src/r_defs.h
+++ b/src/r_defs.h
@@ -355,6 +355,12 @@ enum
 	SECF_NOFALLINGDAMAGE= 2,	// No falling damage in this sector
 	SECF_FLOORDROP		= 4,	// all actors standing on this floor will remain on it when it lowers very fast.
 	SECF_NORESPAWN		= 8,	// players can not respawn in this sector
+
+
+	SECF_WASSECRET		= 1 << 30,	// a secret that was discovered
+	SECF_SECRET			= 1 << 31,	// a secret sector
+
+	SECF_NOMODIFY = SECF_SECRET|SECF_WASSECRET	// not modifiable by Sector_ChangeFlags
 };
 
 enum
@@ -642,6 +648,20 @@ struct sector_t
 		return pos == floor? floorplane:ceilingplane;
 	}
 
+	bool isSecret() const
+	{
+		return !!(Flags & SECF_SECRET);
+	}
+
+	bool wasSecret() const
+	{
+		return !!(Flags & SECF_WASSECRET);
+	}
+
+	void ClearSecret()
+	{
+		Flags &= ~SECF_SECRET;
+	}
 
 	bool PlaneMoving(int pos);
 
@@ -729,7 +749,6 @@ struct sector_t
 	// regular sky.
 	TObjPtr<ASkyViewpoint> FloorSkyBox, CeilingSkyBox;
 
-	short						secretsector;		//jff 2/16/98 remembers if sector WAS secret (automap)
 	int							sectornum;			// for comparing sector copies
 
 	extsector_t	*				e;		// This stores data that requires construction/destruction. Such data must not be copied by R_FakeFlat.
diff --git a/src/version.h b/src/version.h
index d7026786e..b10074f41 100644
--- a/src/version.h
+++ b/src/version.h
@@ -76,7 +76,7 @@ const char *GetVersionString();
 
 // Use 4500 as the base git save version, since it's higher than the
 // SVN revision ever got.
-#define SAVEVER 4528
+#define SAVEVER 4529
 
 #define SAVEVERSTRINGIFY2(x) #x
 #define SAVEVERSTRINGIFY(x) SAVEVERSTRINGIFY2(x)