diff --git a/src/tools/map_convert_07.cpp b/src/tools/map_convert_07.cpp
index ebd6f5678..2794ed0f8 100644
--- a/src/tools/map_convert_07.cpp
+++ b/src/tools/map_convert_07.cpp
@@ -219,14 +219,15 @@ int main(int argc, const char **argv)
 	{
 		int Type, ID;
 		void *pItem = g_DataReader.GetItem(Index, &Type, &ID);
-		int Size = g_DataReader.GetItemSize(Index);
 
-		// filter ITEMTYPE_EX items, they will be automatically added again
-		if(Type == ITEMTYPE_EX)
+		// Filter items with unknown type, as we can't write them back.
+		// Filter ITEMTYPE_EX items, they will be automatically added again.
+		if(Type < 0 || Type == ITEMTYPE_EX)
 		{
 			continue;
 		}
 
+		int Size = g_DataReader.GetItemSize(Index);
 		Success &= CheckImageDimensions(pItem, Type, pSourceFileName);
 
 		CMapItemImage NewImageItem;
diff --git a/src/tools/map_create_pixelart.cpp b/src/tools/map_create_pixelart.cpp
index 52d54d471..18d51b524 100644
--- a/src/tools/map_create_pixelart.cpp
+++ b/src/tools/map_create_pixelart.cpp
@@ -377,8 +377,13 @@ void SaveOutputMap(CDataFileReader &InputMap, CDataFileWriter &OutputMap, CMapIt
 		int ID, Type;
 		void *pItem = InputMap.GetItem(i, &Type, &ID);
 
-		if(Type == ITEMTYPE_EX)
+		// Filter items with unknown type, as we can't write them back.
+		// Filter ITEMTYPE_EX items, they will be automatically added again.
+		if(Type < 0 || Type == ITEMTYPE_EX)
+		{
 			continue;
+		}
+
 		if(i == NewItemNumber)
 			pItem = pNewItem;
 
diff --git a/src/tools/map_optimize.cpp b/src/tools/map_optimize.cpp
index 2da28b1c0..f08334f57 100644
--- a/src/tools/map_optimize.cpp
+++ b/src/tools/map_optimize.cpp
@@ -140,13 +140,14 @@ int main(int argc, const char **argv)
 	{
 		int Type, ID;
 		void *pPtr = Reader.GetItem(Index, &Type, &ID);
-		int Size = Reader.GetItemSize(Index);
 
-		// filter ITEMTYPE_EX items, they will be automatically added again
-		if(Type == ITEMTYPE_EX)
+		// Filter items with unknown type, as we can't write them back.
+		// Filter ITEMTYPE_EX items, they will be automatically added again.
+		if(Type < 0 || Type == ITEMTYPE_EX)
 		{
 			continue;
 		}
+
 		// for all layers, check if it uses a image and set the corresponding flag
 		if(Type == MAPITEMTYPE_LAYER)
 		{
@@ -203,6 +204,7 @@ int main(int argc, const char **argv)
 			++i;
 		}
 
+		int Size = Reader.GetItemSize(Index);
 		Writer.AddItem(Type, ID, Size, pPtr);
 	}
 
diff --git a/src/tools/map_replace_area.cpp b/src/tools/map_replace_area.cpp
index f0d4aed3a..89187922c 100644
--- a/src/tools/map_replace_area.cpp
+++ b/src/tools/map_replace_area.cpp
@@ -168,8 +168,13 @@ void SaveOutputMap(CDataFileReader &InputMap, CDataFileWriter &OutputMap)
 		int ID, Type;
 		void *pItem = InputMap.GetItem(i, &Type, &ID);
 
-		if(Type == ITEMTYPE_EX)
+		// Filter items with unknown type, as we can't write them back.
+		// Filter ITEMTYPE_EX items, they will be automatically added again.
+		if(Type < 0 || Type == ITEMTYPE_EX)
+		{
 			continue;
+		}
+
 		if(g_apNewItem[i])
 			pItem = g_apNewItem[i];
 
diff --git a/src/tools/map_replace_image.cpp b/src/tools/map_replace_image.cpp
index b67ce18ae..01aef691a 100644
--- a/src/tools/map_replace_image.cpp
+++ b/src/tools/map_replace_image.cpp
@@ -150,9 +150,12 @@ int main(int argc, const char **argv)
 		int Type, ID;
 		void *pItem = g_DataReader.GetItem(Index, &Type, &ID);
 
-		// filter ITEMTYPE_EX items, they will be automatically added again
-		if(Type == ITEMTYPE_EX)
+		// Filter items with unknown type, as we can't write them back.
+		// Filter ITEMTYPE_EX items, they will be automatically added again.
+		if(Type < 0 || Type == ITEMTYPE_EX)
+		{
 			continue;
+		}
 
 		int Size = g_DataReader.GetItemSize(Index);
 
diff --git a/src/tools/map_resave.cpp b/src/tools/map_resave.cpp
index 5ff209050..206085198 100644
--- a/src/tools/map_resave.cpp
+++ b/src/tools/map_resave.cpp
@@ -32,9 +32,12 @@ static int ResaveMap(const char *pSourceMap, const char *pDestinationMap, IStora
 		int Type, ID;
 		const void *pPtr = Reader.GetItem(Index, &Type, &ID);
 
-		// filter ITEMTYPE_EX items, they will be automatically added again
-		if(Type == ITEMTYPE_EX)
+		// Filter items with unknown type, as we can't write them back.
+		// Filter ITEMTYPE_EX items, they will be automatically added again.
+		if(Type < 0 || Type == ITEMTYPE_EX)
+		{
 			continue;
+		}
 
 		int Size = Reader.GetItemSize(Index);
 		Writer.AddItem(Type, ID, Size, pPtr);