diff --git a/source/core/maploader.cpp b/source/core/maploader.cpp
index cd36a0c7e..8df554461 100644
--- a/source/core/maploader.cpp
+++ b/source/core/maploader.cpp
@@ -375,6 +375,9 @@ static void insertAllSprites(const char* filename, const vec3_t* pos, int16_t* c
 void engineLoadBoard(const char* filename, int flags, vec3_t* pos, int16_t* ang, int16_t* cursectnum)
 {
 	inputState.ClearAllInput();
+	memset(sector, 0, sizeof(*sector) * MAXSECTORS);
+	memset(wall, 0, sizeof(*wall) * MAXWALLS);
+	memset(sprite, 0, sizeof(*sector) * MAXSPRITES);
 
 	FileReader fr = fileSystem.OpenFileReader(filename);
 	if (!fr.isOpen()) I_Error("Unable to open map %s", filename);
diff --git a/source/games/blood/src/blood.cpp b/source/games/blood/src/blood.cpp
index 9aea146d5..55399119e 100644
--- a/source/games/blood/src/blood.cpp
+++ b/source/games/blood/src/blood.cpp
@@ -112,7 +112,6 @@ void StartLevel(MapRecord* level)
 		}
 	}
 	memset(xsprite, 0, sizeof(xsprite));
-	memset(sprite, 0, kMaxSprites * sizeof(spritetype));
 	//drawLoadingScreen();
 	dbLoadMap(currentLevel->fileName, (int*)&startpos.x, (int*)&startpos.y, (int*)&startpos.z, &startang, &startsectnum, nullptr);
 	SECRET_SetMapName(currentLevel->DisplayName(), currentLevel->name);
diff --git a/source/games/blood/src/db.cpp b/source/games/blood/src/db.cpp
index 5df48a6fc..4900a9614 100644
--- a/source/games/blood/src/db.cpp
+++ b/source/games/blood/src/db.cpp
@@ -512,6 +512,10 @@ void dbLoadMap(const char *pPath, int *pX, int *pY, int *pZ, short *pAngle, shor
     gModernMap = false;
     #endif
 
+    memset(sector, 0, sizeof(*sector) * MAXSECTORS);
+    memset(wall, 0, sizeof(*wall) * MAXWALLS);
+    memset(sprite, 0, sizeof(*sector) * MAXSPRITES);
+
 #ifdef USE_OPENGL
     Polymost::Polymost_prepare_loadboard();
 #endif
diff --git a/source/games/duke/src/premap.cpp b/source/games/duke/src/premap.cpp
index 97c0d65e7..dbe8c2e71 100644
--- a/source/games/duke/src/premap.cpp
+++ b/source/games/duke/src/premap.cpp
@@ -924,7 +924,7 @@ static void SpawnPortals()
                         if (findwallbetweensectors(i, t) >= 0)
                         {
                             sector[i].portalflags = PORTAL_SECTOR_FLOOR;
-                            sector[i].portalnum = uint8_t(&pt - allPortals.Data());
+                            sector[i].portalnum = uint8_t(1 ^ (&pt - allPortals.Data()));
                             pt.targets.Push(i);
                             goto nexti;
                         }
@@ -943,7 +943,7 @@ static void SpawnPortals()
                         if (findwallbetweensectors(i, t) >= 0)
                         {
                             sector[i].portalflags = PORTAL_SECTOR_CEILING;
-                            sector[i].portalnum = uint8_t(&pt - allPortals.Data());
+                            sector[i].portalnum = uint8_t(1 ^ (&pt - allPortals.Data()));
                             pt.targets.Push(i);
                             goto nexti;
                         }