diff --git a/src/d_main.cpp b/src/d_main.cpp
index 78421e707f..64d29bb550 100644
--- a/src/d_main.cpp
+++ b/src/d_main.cpp
@@ -1920,7 +1920,7 @@ void GetReserved(LumpFilterInfo& lfi)
 {
 	lfi.reservedFolders = { "flats/", "textures/", "hires/", "sprites/", "voxels/", "colormaps/", "acs/", "maps/", "voices/", "patches/", "graphics/", "sounds/", "music/",
 	"materials/", "models/", "fonts/", "brightmaps/" };
-	lfi.requiredPrefixes = { "mapinfo", "zmapinfo", "umapinfo", "gameinfo", "sndinfo", "sndseq", "sbarinfo", "menudef", "gldefs", "animdefs", "decorate", "zscript", "iwadinfo", "maps/" };
+	lfi.requiredPrefixes = { "mapinfo", "zmapinfo", "umapinfo", "gameinfo", "sndinfo", "sndseq", "sbarinfo", "menudef", "gldefs", "animdefs", "decorate", "zscript", "iwadinfo", "complvl", "terrain", "maps/" };
 }
 
 static FString CheckGameInfo(std::vector<std::string> & pwads)
diff --git a/src/doomdef.h b/src/doomdef.h
index 5d70ecd206..111bf7ad2c 100644
--- a/src/doomdef.h
+++ b/src/doomdef.h
@@ -213,7 +213,7 @@ enum : unsigned int
 	COMPATF_VILEGHOSTS		= 1 << 25,	// Crushed monsters are resurrected as ghosts.
 	COMPATF_NOBLOCKFRIENDS	= 1 << 26,	// Friendly monsters aren't blocked by monster-blocking lines.
 	COMPATF_SPRITESORT		= 1 << 27,	// Invert sprite sorting order for sprites of equal distance
-	COMPATF_HITSCAN			= 1 << 28,	// Hitscans use original blockmap anf hit check code.
+	COMPATF_HITSCAN			= 1 << 28,	// Hitscans use original blockmap and hit check code.
 	COMPATF_LIGHT			= 1 << 29,	// Find neighboring light level like Doom
 	COMPATF_POLYOBJ			= 1 << 30,	// Draw polyobjects the old fashioned way
 	COMPATF_MASKEDMIDTEX	= 1u << 31,	// Ignore compositing when drawing masked midtextures
diff --git a/src/gamedata/g_mapinfo.cpp b/src/gamedata/g_mapinfo.cpp
index a525e80d94..1fec3346bc 100644
--- a/src/gamedata/g_mapinfo.cpp
+++ b/src/gamedata/g_mapinfo.cpp
@@ -2587,6 +2587,56 @@ void G_ParseMapInfo (FString basemapinfo)
 	int lump, lastlump = 0;
 	level_info_t gamedefaults;
 
+	int flags1 = 0, flags2 = 0;
+	if (gameinfo.gametype == GAME_Doom)
+	{
+		int comp = fileSystem.CheckNumForName("COMPLVL");
+		if (comp >= 0)
+		{
+			auto complvl = fileSystem.ReadFile(comp);
+			auto data = complvl.GetString();
+			int length = fileSystem.FileLength(comp);
+			if (length == 7 && !strnicmp("vanilla", data, 7))
+			{
+				flags1 = 
+					COMPATF_SHORTTEX | COMPATF_STAIRINDEX | COMPATF_USEBLOCKING | COMPATF_NODOORLIGHT | COMPATF_SPRITESORT |
+					COMPATF_TRACE | COMPATF_MISSILECLIP | COMPATF_SOUNDTARGET | COMPATF_DEHHEALTH | COMPATF_CROSSDROPOFF |
+					COMPATF_LIGHT | COMPATF_MASKEDMIDTEX |
+					COMPATF_LIMITPAIN | COMPATF_INVISIBILITY | COMPATF_VILEGHOSTS;
+
+				flags2 =
+					COMPATF2_FLOORMOVE | COMPATF2_EXPLODE1 | COMPATF2_NOMBF21 | COMPATF2_POINTONLINE;
+			}
+			else if (length == 4 && !strnicmp("boom", data, 4))
+			{
+				flags1 =
+					COMPATF_TRACE | COMPATF_SOUNDTARGET | COMPATF_BOOMSCROLL | COMPATF_MISSILECLIP | COMPATF_MASKEDMIDTEX |
+					COMPATF_INVISIBILITY;
+
+				flags2 =
+					COMPATF2_EXPLODE1 | COMPATF2_NOMBF21 | COMPATF2_POINTONLINE;
+			}
+			else if (length == 3 && !strnicmp("mbf", data, 3))
+			{
+				flags1 =
+					COMPATF_TRACE | COMPATF_SOUNDTARGET | COMPATF_BOOMSCROLL | COMPATF_MISSILECLIP | COMPATF_MUSHROOM |
+					COMPATF_MBFMONSTERMOVE | COMPATF_NOBLOCKFRIENDS | COMPATF_MASKEDMIDTEX | COMPATF_INVISIBILITY;
+
+				flags2 =
+					COMPATF2_EXPLODE1 | COMPATF2_AVOID_HAZARDS | COMPATF2_STAYONLIFT | COMPATF2_NOMBF21 | COMPATF2_POINTONLINE;
+			}
+			else if (length == 5 && !strnicmp("mbf21", data, 5))
+			{
+				flags1 =
+					COMPATF_TRACE | COMPATF_SOUNDTARGET | COMPATF_BOOMSCROLL | COMPATF_MISSILECLIP | COMPATF_MUSHROOM |
+					COMPATF_MASKEDMIDTEX | COMPATF_INVISIBILITY;
+
+				flags2 =
+					COMPATF2_EXPLODE1 | COMPATF2_AVOID_HAZARDS | COMPATF2_STAYONLIFT | COMPATF2_POINTONLINE;
+			}
+		}
+	}
+
 	// Parse the default MAPINFO for the current game. This lump *MUST* come from zdoom.pk3.
 	if (basemapinfo.IsNotEmpty())
 	{
@@ -2600,7 +2650,11 @@ void G_ParseMapInfo (FString basemapinfo)
 		}
 		parse.ParseMapInfo(baselump, gamedefaults, defaultinfo);
 	}
-
+	gamedefaults.compatflags |= flags1;
+	gamedefaults.compatmask |= flags1;
+	gamedefaults.compatflags2 |= flags2;
+	gamedefaults.compatmask2 |= flags2;
+	
 	static const char *mapinfonames[] = { "MAPINFO", "ZMAPINFO", "UMAPINFO", NULL };
 	int nindex;