diff --git a/Source/CMakeLists.txt b/Source/CMakeLists.txt
index a76a8f125..187754ba7 100644
--- a/Source/CMakeLists.txt
+++ b/Source/CMakeLists.txt
@@ -142,6 +142,8 @@ set(libdevilutionx_SRCS
 
   platform/locale.cpp
 
+  portals/validation.cpp
+
   qol/autopickup.cpp
   qol/chatlog.cpp
   qol/floatingnumbers.cpp
diff --git a/Source/control.cpp b/Source/control.cpp
index ca861e65d..07b21caf4 100644
--- a/Source/control.cpp
+++ b/Source/control.cpp
@@ -422,12 +422,6 @@ void AppendArenaOverview(std::string &ret)
 	}
 }
 
-const dungeon_type DungeonTypeForArena[] = {
-	dungeon_type::DTYPE_CATHEDRAL, // SL_ARENA_CHURCH
-	dungeon_type::DTYPE_HELL,      // SL_ARENA_HELL
-	dungeon_type::DTYPE_HELL,      // SL_ARENA_CIRCLE_OF_LIFE
-};
-
 std::string TextCmdArena(const std::string_view parameter)
 {
 	std::string ret;
@@ -455,7 +449,7 @@ std::string TextCmdArena(const std::string_view parameter)
 		return ret;
 	}
 
-	setlvltype = DungeonTypeForArena[arenaLevel - SL_FIRST_ARENA];
+	setlvltype = GetArenaLevelType(arenaLevel);
 	StartNewLvl(*MyPlayer, WM_DIABSETLVL, arenaLevel);
 	return ret;
 }
diff --git a/Source/levels/setmaps.h b/Source/levels/setmaps.h
index 0d2a8fe51..59cc0a93a 100644
--- a/Source/levels/setmaps.h
+++ b/Source/levels/setmaps.h
@@ -5,8 +5,26 @@
  */
 #pragma once
 
+#include "levels/gendung.h"
+
 namespace devilution {
 
+/**
+ * @brief Get the tile type used to render the given arena level
+ */
+inline dungeon_type GetArenaLevelType(_setlevels arenaLevel)
+{
+	constexpr dungeon_type DungeonTypeForArena[] = {
+		dungeon_type::DTYPE_CATHEDRAL, // SL_ARENA_CHURCH
+		dungeon_type::DTYPE_HELL,      // SL_ARENA_HELL
+		dungeon_type::DTYPE_HELL,      // SL_ARENA_CIRCLE_OF_LIFE
+	};
+
+	constexpr size_t arenaCount = sizeof(DungeonTypeForArena) / sizeof(dungeon_type);
+	const size_t index = arenaLevel - SL_FIRST_ARENA;
+	return index < arenaCount ? DungeonTypeForArena[index] : DTYPE_NONE;
+}
+
 /**
  * @brief Load a quest map, the given map is specified via the global setlvlnum
  */
diff --git a/Source/msg.cpp b/Source/msg.cpp
index c64524a02..9893f3c24 100644
--- a/Source/msg.cpp
+++ b/Source/msg.cpp
@@ -39,6 +39,7 @@
 #include "pack.h"
 #include "pfile.h"
 #include "plrmsg.h"
+#include "portals/validation.hpp"
 #include "spells.h"
 #include "storm/storm_net.hpp"
 #include "sync.h"
@@ -289,6 +290,12 @@ Item ItemLimbo;
 /** @brief Last sent player command for the local player. */
 TCmdLocParam5 lastSentPlayerCmd;
 
+bool IsPortalDeltaValid(const DPortal &portal)
+{
+	const WorldTilePosition position { portal.x, portal.y };
+	return IsPortalDeltaValid(position, portal.level, portal.ltype, portal.setlvl);
+}
+
 uint8_t GetLevelForMultiplayer(uint8_t level, bool isSetLevel)
 {
 	if (isSetLevel)
@@ -689,6 +696,8 @@ const std::byte *DeltaImportJunk(const std::byte *src, const std::byte *end)
 			if (src + sizeof(DPortal) > end)
 				return nullptr;
 			memcpy(&sgJunk.portal[i], src, sizeof(DPortal));
+			if (!IsPortalDeltaValid(sgJunk.portal[i]))
+				memset(&sgJunk.portal[i], 0xFF, sizeof(DPortal));
 			src += sizeof(DPortal);
 		}
 	}
diff --git a/Source/portals/validation.cpp b/Source/portals/validation.cpp
new file mode 100644
index 000000000..0557fb2aa
--- /dev/null
+++ b/Source/portals/validation.cpp
@@ -0,0 +1,49 @@
+/**
+ * @file portals/validation.cpp
+ *
+ * Implementation of functions for validation of portal data.
+ */
+
+#include "portals/validation.hpp"
+
+#include <cstdint>
+
+#include "engine/world_tile.hpp"
+#include "levels/gendung.h"
+#include "levels/setmaps.h"
+#include "quests.h"
+
+namespace devilution {
+
+namespace {
+
+dungeon_type GetQuestLevelType(_setlevels questLevel)
+{
+	for (const Quest &quest : Quests) {
+		if (quest._qslvl == questLevel)
+			return quest._qlvltype;
+	}
+	return DTYPE_NONE;
+}
+
+dungeon_type GetSetLevelType(_setlevels setLevel)
+{
+	bool isArenaLevel = setLevel >= SL_FIRST_ARENA && setLevel <= SL_LAST;
+	return isArenaLevel ? GetArenaLevelType(setLevel) : GetQuestLevelType(setLevel);
+}
+
+} // namespace
+
+bool IsPortalDeltaValid(WorldTilePosition location, uint8_t level, uint8_t ltype, bool isOnSetLevel)
+{
+	if (!InDungeonBounds(location))
+		return false;
+	dungeon_type levelType = static_cast<dungeon_type>(ltype);
+	if (levelType == DTYPE_NONE)
+		return false;
+	if (isOnSetLevel)
+		return levelType == GetSetLevelType(static_cast<_setlevels>(level));
+	return levelType == GetLevelType(level);
+}
+
+} // namespace devilution
diff --git a/Source/portals/validation.hpp b/Source/portals/validation.hpp
new file mode 100644
index 000000000..c0e2c3c30
--- /dev/null
+++ b/Source/portals/validation.hpp
@@ -0,0 +1,16 @@
+/**
+ * @file portals/validation.hpp
+ *
+ * Interface of functions for validation of portal data.
+ */
+#pragma once
+
+#include <cstdint>
+
+#include "engine/world_tile.hpp"
+
+namespace devilution {
+
+bool IsPortalDeltaValid(WorldTilePosition location, uint8_t level, uint8_t levelType, bool isOnSetLevel);
+
+} // namespace devilution