diff --git a/src/deh_soc.c b/src/deh_soc.c
index fdba5c507..241ddb8eb 100644
--- a/src/deh_soc.c
+++ b/src/deh_soc.c
@@ -878,6 +878,28 @@ void readgametype(MYFILE *f, char *gtname)
 		I_Error("Out of Gametype Freeslots while allocating \"%s\"\nLoad less addons to fix this.", gtname);
 	}
 
+	if (gtname[0] == '\0')
+	{
+		deh_warning("Custom gametype must have a name");
+		return;
+	}
+
+	if (strlen(gtname) >= MAXGAMETYPELENGTH)
+	{
+		deh_warning("Custom gametype \"%s\"'s name must be %d long at most", gtname, MAXGAMETYPELENGTH-1);
+		return;
+	}
+
+	for (i = 0; i < numgametypes; i++)
+		if (fastcmp(gtname, gametypes[i]->name))
+			break;
+
+	if (i < numgametypes)
+	{
+		deh_warning("Custom gametype \"%s\"'s name is already in use", gtname);
+		return;
+	}
+
 	// Add the new gametype
 	newgametype = Z_Calloc(sizeof (gametype_t), PU_STATIC, NULL);
 	if (!newgametype)
diff --git a/src/doomstat.h b/src/doomstat.h
index 63739358f..e7ff2f093 100644
--- a/src/doomstat.h
+++ b/src/doomstat.h
@@ -450,6 +450,7 @@ extern INT32 nummapheaders, mapallocsize;
 
 // Gametypes
 #define NUMGAMETYPEFREESLOTS (MAXGAMETYPES-GT_FIRSTFREESLOT)
+#define MAXGAMETYPELENGTH 32
 
 enum GameType
 {
diff --git a/src/g_demo.c b/src/g_demo.c
index ddf0b342f..f82e96325 100644
--- a/src/g_demo.c
+++ b/src/g_demo.c
@@ -2378,7 +2378,9 @@ void G_BeginRecording(void)
 	M_Memcpy(demo_p, mapmd5, 16); demo_p += 16;
 
 	WRITEUINT8(demo_p, demoflags);
-	WRITEUINT8(demo_p, gametype & 0xFF);
+
+	WRITESTRINGN(demo_p, gametypes[gametype]->name, MAXGAMETYPELENGTH);
+
 	WRITEUINT8(demo_p, numlaps);
 
 	// file list
@@ -2652,7 +2654,7 @@ UINT8 G_CmpDemoTime(char *oldname, char *newname)
 	SKIPSTRING(p); // gamemap
 	p += 16; // map md5
 	flags = READUINT8(p); // demoflags
-	p++; // gametype
+	SKIPSTRING(p); // gametype
 	p++; // numlaps
 	G_SkipDemoExtraFiles(&p);
 
@@ -2711,7 +2713,7 @@ UINT8 G_CmpDemoTime(char *oldname, char *newname)
 	SKIPSTRING(p); // gamemap
 	p += 16; // mapmd5
 	flags = READUINT8(p);
-	p++; // gametype
+	SKIPSTRING(p); // gametype
 	p++; // numlaps
 	G_SkipDemoExtraFiles(&p);
 	if (!(flags & aflags))
@@ -2756,7 +2758,7 @@ void G_LoadDemoInfo(menudemo_t *pdemo)
 	UINT8 version, subversion, pdemoflags, worknumskins, skinid;
 	democharlist_t *skinlist = NULL;
 	UINT16 pdemoversion, count;
-	char mapname[MAXMAPLUMPNAME];
+	char mapname[MAXMAPLUMPNAME],gtname[MAXGAMETYPELENGTH];
 	INT32 i;
 
 	if (!FIL_ReadFile(pdemo->filepath, &infobuffer))
@@ -2820,7 +2822,9 @@ void G_LoadDemoInfo(menudemo_t *pdemo)
 		return;
 	}
 
-	pdemo->gametype = READUINT8(info_p);
+	READSTRINGN(info_p, gtname, sizeof(gtname)); // gametype
+	pdemo->gametype = G_GetGametypeByName(gtname);
+
 	pdemo->numlaps = READUINT8(info_p);
 
 	pdemo->addonstatus = G_CheckDemoExtraFiles(&info_p, true);
@@ -2932,9 +2936,11 @@ void G_DeferedPlayDemo(const char *name)
 
 void G_DoPlayDemo(char *defdemoname)
 {
-	UINT8 i, p, numslots = 0;
+	INT32 i;
+	UINT8 p, numslots = 0;
 	lumpnum_t l;
-	char color[MAXCOLORNAME+1],follower[17],mapname[MAXMAPLUMPNAME],*n,*pdemoname;
+	char color[MAXCOLORNAME+1],follower[17],mapname[MAXMAPLUMPNAME],gtname[MAXGAMETYPELENGTH];
+	char *n,*pdemoname;
 	UINT8 availabilities[MAXPLAYERS][MAXAVAILABILITY];
 	UINT8 version,subversion;
 	UINT32 randseed[PRNUMCLASS];
@@ -2951,6 +2957,7 @@ void G_DoPlayDemo(char *defdemoname)
 
 	follower[16] = '\0';
 	color[MAXCOLORNAME] = '\0';
+	gtname[MAXGAMETYPELENGTH-1] = '\0';
 
 	// No demo name means we're restarting the current demo
 	if (defdemoname == NULL)
@@ -3060,8 +3067,22 @@ void G_DoPlayDemo(char *defdemoname)
 	demo_p += 16; // mapmd5
 
 	demoflags = READUINT8(demo_p);
-	gametype = READUINT8(demo_p);
-	G_SetGametype(gametype);
+
+	READSTRINGN(demo_p, gtname, sizeof(gtname)); // gametype
+	i = G_GetGametypeByName(gtname);
+	if (i < 0)
+	{
+		snprintf(msg, 1024, M_GetText("%s is in a gametype that is not currently loaded and cannot be played.\n"), pdemoname);
+		CONS_Alert(CONS_ERROR, "%s", msg);
+		M_StartMessage(msg, NULL, MM_NOTHING);
+		Z_Free(pdemoname);
+		Z_Free(demobuffer);
+		demo.playback = false;
+		demo.title = false;
+		return;
+	}
+	G_SetGametype(i);
+
 	numlaps = READUINT8(demo_p);
 
 	if (demo.title) // Titledemos should always play and ought to always be compatible with whatever wadlist is running.
@@ -3519,7 +3540,7 @@ void G_AddGhost(char *defdemoname)
 		return;
 	}
 
-	p++; // gametype
+	SKIPSTRING(p); // gametype
 	p++; // numlaps
 	G_SkipDemoExtraFiles(&p); // Don't wanna modify the file list for ghosts.
 
@@ -3736,7 +3757,7 @@ void G_UpdateStaffGhostName(lumpnum_t l)
 		goto fail; // we don't NEED to do it here, but whatever
 	}
 
-	p++; // Gametype
+	SKIPSTRING(p); // gametype
 	p++; // numlaps
 	G_SkipDemoExtraFiles(&p);
 
diff --git a/src/g_demo.h b/src/g_demo.h
index db5158b9a..8ecf08448 100644
--- a/src/g_demo.h
+++ b/src/g_demo.h
@@ -84,7 +84,7 @@ struct menudemo_t {
 	char title[65]; // Null-terminated for string prints
 	UINT16 map;
 	UINT8 addonstatus; // What do we need to do addon-wise to play this demo?
-	UINT8 gametype;
+	INT16 gametype;
 	SINT8 kartspeed; // Add OR DF_ENCORE for encore mode, idk
 	UINT8 numlaps;
 
diff --git a/src/k_menudraw.c b/src/k_menudraw.c
index 1a3f7a8d8..f47689f8b 100644
--- a/src/k_menudraw.c
+++ b/src/k_menudraw.c
@@ -3969,9 +3969,11 @@ static void M_DrawReplayHutReplayInfo(menudemo_t *demoref)
 			V_DrawThinString(x, y+9, V_SNAPTOTOP|V_ALLOWLOWERCASE, va("(%d laps)", demoref->numlaps));
 
 		{
-			const char *gtstring = "???";
-			if (demoref->gametype >= GT_FIRSTFREESLOT)
-				; // TODO: Support custom gametypes in netreplays (would require deeper changes than this)
+			const char *gtstring;
+			if (demoref->gametype < 0)
+			{
+				gtstring = "Custom (not loaded)";
+			}
 			else
 			{
 				gtstring = gametypes[demoref->gametype]->name;
@@ -3994,7 +3996,7 @@ static void M_DrawReplayHutReplayInfo(menudemo_t *demoref)
 		V_DrawThinString(x, y+29, V_SNAPTOTOP|highlightflags, "WINNER");
 		V_DrawString(x+38, y+30, V_SNAPTOTOP|V_ALLOWLOWERCASE, demoref->standings[0].name);
 
-		if (demoref->gametype < GT_FIRSTFREESLOT)
+		if (demoref->gametype >= 0)
 		{
 			if (gametypes[demoref->gametype]->rules & GTR_POINTLIMIT)
 			{
@@ -4215,7 +4217,7 @@ void M_DrawReplayStartMenu(void)
 
 		if (demoref->standings[i].timeorscore == UINT32_MAX-1)
 			V_DrawThinString(BASEVIDWIDTH-92, STARTY + i*20 + 9, V_SNAPTOTOP, "NO CONTEST");
-		else if (demoref->gametype >= GT_FIRSTFREESLOT)
+		else if (demoref->gametype < 0)
 			;
 		else if (gametypes[demoref->gametype]->rules & GTR_POINTLIMIT)
 			V_DrawString(BASEVIDWIDTH-92, STARTY + i*20 + 9, V_SNAPTOTOP, va("%d", demoref->standings[i].timeorscore));
diff --git a/src/lua_baselib.c b/src/lua_baselib.c
index 61587bd62..1a33438fb 100644
--- a/src/lua_baselib.c
+++ b/src/lua_baselib.c
@@ -2980,6 +2980,7 @@ static int lib_gAddGametype(lua_State *L)
 	INT32 newgtpointlimit = 0;
 	INT32 newgttimelimit = 0;
 	UINT8 newgtinttype = 0;
+	INT16 j;
 
 	luaL_checktype(L, 1, LUA_TTABLE);
 	lua_settop(L, 1); // Clear out all other possible arguments, leaving only the first one.
@@ -3043,13 +3044,22 @@ static int lib_gAddGametype(lua_State *L)
 #undef FIELDERROR
 #undef TYPEERROR
 
+	if (gtname == NULL)
+		return luaL_error(L, "Custom gametype must have a name");
+
+	if (strlen(gtname) >= MAXGAMETYPELENGTH)
+		return luaL_error(L, "Custom gametype \"%s\"'s name must be %d long at most", gtname, MAXGAMETYPELENGTH-1);
+
+	for (j = 0; j < numgametypes; j++)
+		if (!strcmp(gtname, gametypes[j]->name))
+			break;
+
+	if (j < numgametypes)
+		return luaL_error(L, "Custom gametype \"%s\"'s name is already in use", gtname);
+
 	// pop gametype table
 	lua_pop(L, 1);
 
-	// Set defaults
-	if (gtname == NULL)
-		gtname = Z_StrDup("Unnamed gametype");
-
 	// Add the new gametype
 	newgametype = Z_Calloc(sizeof (gametype_t), PU_STATIC, NULL);
 	if (!newgametype)