diff --git a/src/d_main.c b/src/d_main.c
index e28dc1c5c..ec4fe5425 100644
--- a/src/d_main.c
+++ b/src/d_main.c
@@ -1132,9 +1132,9 @@ D_ConvertVersionNumbers (void)
 //
 void D_SRB2Main(void)
 {
+	INT32 numbasemapheaders;
 	INT32 i;
 	UINT16 wadnum;
-	lumpinfo_t *lumpinfo;
 	char *name;
 
 	INT32 p;
@@ -1397,31 +1397,7 @@ void D_SRB2Main(void)
 
 #endif //ifndef DEVELOP
 
-	//
-	// search for maps
-	//
-	for (wadnum = 4; wadnum < 6; wadnum++) // fucking arbitrary numbers
-	{
-		lumpinfo = wadfiles[wadnum]->lumpinfo;
-		for (i = 0; i < wadfiles[wadnum]->numlumps; i++, lumpinfo++)
-		{
-			name = lumpinfo->name;
-
-			if (name[0] == 'M' && name[1] == 'A' && name[2] == 'P') // Ignore the headers
-			{
-				INT16 num;
-				if (name[5] != '\0')
-					continue;
-				num = (INT16)M_MapNumber(name[3], name[4]);
-
-				// we want to record whether this map exists. if it doesn't have a header, we can assume it's not relephant
-				if (num <= NUMMAPS && mapheaderinfo[num - 1])
-				{
-					mapheaderinfo[num - 1]->alreadyExists = true;
-				}
-			}
-		}
-	}
+	numbasemapheaders = nummapheaders;
 
 	CON_SetLoadingProgress(LOADED_IWAD);
 
@@ -1430,32 +1406,17 @@ void D_SRB2Main(void)
 	D_CleanFile(startuppwads);
 
 	//
-	// search for maps... again.
+	// search for maps
 	//
 	for (wadnum = mainwads+1; wadnum < numwadfiles; wadnum++)
 	{
-		lumpinfo = wadfiles[wadnum]->lumpinfo;
-		for (i = 0; i < wadfiles[wadnum]->numlumps; i++, lumpinfo++)
+		for (i = 0; i < numbasemapheaders; ++i)
 		{
-			name = lumpinfo->name;
+			name = mapheaderinfo[i]->lumpname;
 
-			if (name[0] == 'M' && name[1] == 'A' && name[2] == 'P') // Ignore the headers
+			if (W_CheckNumForMapPwad(name, wadnum, 0) != INT16_MAX)
 			{
-				INT16 num;
-				if (name[5] != '\0')
-					continue;
-				num = (INT16)M_MapNumber(name[3], name[4]);
-
-				// we want to record whether this map exists. if it doesn't have a header, we can assume it's not relephant
-				if (num <= NUMMAPS && mapheaderinfo[num - 1])
-				{
-					if (mapheaderinfo[num - 1]->alreadyExists != false)
-					{
-						G_SetGameModified(multiplayer, true); // oops, double-defined - no record attack privileges for you
-					}
-
-					mapheaderinfo[num - 1]->alreadyExists = true;
-				}
+				G_SetGameModified(multiplayer, true); // oops, double-defined - no record attack privileges for you
 
 				CONS_Printf("%s\n", name);
 			}
diff --git a/src/doomstat.h b/src/doomstat.h
index 91ca7b0ea..7f9dcac93 100644
--- a/src/doomstat.h
+++ b/src/doomstat.h
@@ -395,9 +395,6 @@ typedef struct
 
 	SINT8 musforcereset; ///< Force resetmusic (-1 for default; 0 for force off; 1 for force on)
 
-	// SRB2Kart: Keeps track of if a map lump exists, so we can tell when a map is being replaced.
-	boolean alreadyExists;
-
 	// Lua stuff.
 	// (This is not ifdeffed so the map header structure can stay identical, just in case.)
 	UINT8 numCustomOptions;     ///< Internal. For Lua custom value support.
diff --git a/src/g_demo.c b/src/g_demo.c
index a841afa9e..89846d1a9 100644
--- a/src/g_demo.c
+++ b/src/g_demo.c
@@ -2840,7 +2840,7 @@ void G_DoPlayDemo(char *defdemoname)
 	demo_p += 4; // Extrainfo location
 
 	// ...*map* not loaded?
-	if (!gamemap || (gamemap > NUMMAPS) || !mapheaderinfo[gamemap-1] || !(mapheaderinfo[gamemap-1]->alreadyExists == true))
+	if (!gamemap || (gamemap > NUMMAPS) || !mapheaderinfo[gamemap-1])
 	{
 		snprintf(msg, 1024, M_GetText("%s features a course that is not currently loaded.\n"), pdemoname);
 		CONS_Alert(CONS_ERROR, "%s", msg);
diff --git a/src/p_setup.c b/src/p_setup.c
index 4a50e2d08..d44b477bc 100644
--- a/src/p_setup.c
+++ b/src/p_setup.c
@@ -351,8 +351,6 @@ static void P_ClearSingleMapHeaderInfo(INT16 i)
 {
 	const INT16 num = (INT16)(i-1);
 
-	boolean exists = (mapheaderinfo[gamemap-1]->alreadyExists == true);
-
 	mapheaderinfo[num]->lvlttl[0] = '\0';
 	mapheaderinfo[num]->selectheading[0] = '\0';
 	mapheaderinfo[num]->subttl[0] = '\0';
@@ -411,9 +409,6 @@ static void P_ClearSingleMapHeaderInfo(INT16 i)
 #endif
 	P_DeleteGrades(num);
 
-	// see p_setup.c - prevents replacing maps in addons with different versions
-	mapheaderinfo[num]->alreadyExists = exists;
-
 	mapheaderinfo[num]->customopts = NULL;
 	mapheaderinfo[num]->numCustomOptions = 0;
 }
@@ -4317,6 +4312,8 @@ static lumpinfo_t* FindFolder(const char *folName, UINT16 *start, UINT16 *end, l
 boolean P_AddWadFile(const char *wadfilename)
 {
 	size_t i, j, sreplaces = 0, mreplaces = 0, digmreplaces = 0;
+	INT32 numexistingmapheaders = nummapheaders;
+	INT32 map;
 	UINT16 numlumps, wadnum;
 	char *name;
 	lumpinfo_t *lumpinfo;
@@ -4466,36 +4463,23 @@ boolean P_AddWadFile(const char *wadfilename)
 	//
 	// search for maps
 	//
-	lumpinfo = wadfiles[wadnum]->lumpinfo;
-	for (i = 0; i < numlumps; i++, lumpinfo++)
+	for (map = 0; map < numexistingmapheaders; ++map)
 	{
-		name = lumpinfo->name;
-		if (name[0] == 'M' && name[1] == 'A' && name[2] == 'P') // Ignore the headers
+		name = mapheaderinfo[map]->lumpname;
+
+		if (W_CheckNumForMapPwad(name, wadnum, 0) != INT16_MAX)
 		{
-			INT16 num;
-			if (name[5]!='\0')
-				continue;
-			num = (INT16)G_MapNumber(name);
-
-			// we want to record whether this map exists. if it doesn't have a header, we can assume it's not relephant
-			if (num <= NUMMAPS && mapheaderinfo[num-1])
-			{
-				if (mapheaderinfo[num - 1]->alreadyExists != false)
-				{
-					G_SetGameModified(multiplayer, true); // oops, double-defined - no record attack privileges for you
-				}
-
-				mapheaderinfo[num - 1]->alreadyExists = true;
-			}
+			G_SetGameModified(multiplayer, true); // oops, double-defined - no record attack privileges for you
 
 			//If you replaced the map you're on, end the level when done.
-			if (num == gamemap)
+			if (map == gamemap - 1)
 				replacedcurrentmap = true;
 
 			CONS_Printf("%s\n", name);
 			mapsadded = true;
 		}
 	}
+
 	if (!mapsadded)
 		CONS_Printf(M_GetText("No maps added\n"));