diff --git a/src/d_main.cpp b/src/d_main.cpp
index 925d2c852..15d5729c9 100644
--- a/src/d_main.cpp
+++ b/src/d_main.cpp
@@ -1506,8 +1506,7 @@ void D_SRB2Main(void)
 	// conversion sometimes needs the palette
 	V_ReloadPalette();
 
-	P_InitMapData();
-	basenummapheaders = nummapheaders;
+	P_InitMapData(false);
 
 	CON_SetLoadingProgress(LOADED_IWAD);
 
@@ -1566,7 +1565,7 @@ void D_SRB2Main(void)
 		//
 		// search for pwad maps
 		//
-		P_InitMapData();
+		P_InitMapData(true);
 		HU_LoadGraphics();
 	}
 
diff --git a/src/doomstat.h b/src/doomstat.h
index 8eaf86de1..12739ce25 100644
--- a/src/doomstat.h
+++ b/src/doomstat.h
@@ -449,7 +449,7 @@ struct mapheader_t
 #define LF2_VISITNEEDED   (1<<3) ///< Not available in Time Attack modes until you visit the level
 
 extern mapheader_t** mapheaderinfo;
-extern INT32 nummapheaders, basenummapheaders, mapallocsize;
+extern INT32 nummapheaders, mapallocsize;
 
 #define MAXMAPLUMPNAME 64 // includes \0, for cleaner savedata
 
diff --git a/src/g_game.c b/src/g_game.c
index 030350d1f..dd4176fd5 100644
--- a/src/g_game.c
+++ b/src/g_game.c
@@ -184,7 +184,6 @@ struct quake quake;
 // Map Header Information
 mapheader_t** mapheaderinfo = {NULL};
 INT32 nummapheaders, mapallocsize = 0;
-INT32 basenummapheaders = 0;
 
 // Kart cup definitions
 cupheader_t *kartcupheaders = NULL;
diff --git a/src/p_setup.c b/src/p_setup.c
index dd7132ba7..43425c35a 100644
--- a/src/p_setup.c
+++ b/src/p_setup.c
@@ -8674,7 +8674,7 @@ lumpnum_t wadnamelump = LUMPERROR;
 INT16 wadnamemap = 0; // gamemap based
 
 // Initialising map data...
-UINT8 P_InitMapData(void)
+UINT8 P_InitMapData(boolean existingmapheaders)
 {
 	UINT8 ret = 0;
 	INT32 i;
@@ -8691,7 +8691,15 @@ UINT8 P_InitMapData(void)
 
 		// Doesn't exist?
 		if (maplump == INT16_MAX)
+		{
+#ifndef DEVELOP
+			if (!existingmapheaders)
+			{
+				I_Error("P_InitMapData: Base map %s has a header but no level\n", name);
+			}
+#endif
 			continue;
+		}
 
 		// No change?
 		if (mapheaderinfo[i]->lumpnum == maplump)
@@ -8701,7 +8709,7 @@ UINT8 P_InitMapData(void)
 		{
 			ret |= MAPRET_ADDED;
 
-			if (basenummapheaders)
+			if (existingmapheaders)
 			{
 				CONS_Printf("%s\n", name);
 
@@ -8714,6 +8722,7 @@ UINT8 P_InitMapData(void)
 						ret |= MAPRET_CURRENTREPLACED;
 				}
 			}
+
 			mapheaderinfo[i]->lumpnum = maplump;
 			if (maplump == wadnamelump)
 				wadnamemap = i+1;
@@ -9008,7 +9017,7 @@ boolean P_MultiSetupWadFiles(boolean fullsetup)
 
 	if (partadd_stage == 2)
 	{
-		UINT8 mapsadded = P_InitMapData();
+		UINT8 mapsadded = P_InitMapData(true);
 
 		if (!mapsadded)
 			CONS_Printf(M_GetText("No maps added\n"));
diff --git a/src/p_setup.h b/src/p_setup.h
index e4d33d9c0..70b93d532 100644
--- a/src/p_setup.h
+++ b/src/p_setup.h
@@ -113,7 +113,7 @@ boolean P_AddWadFile(const char *wadfilename, wadcompat_t compat);
 
 #define MAPRET_ADDED (1)
 #define MAPRET_CURRENTREPLACED (1<<1)
-UINT8 P_InitMapData(void);
+UINT8 P_InitMapData(boolean existingmapheaders);
 extern lumpnum_t wadnamelump;
 extern INT16 wadnamemap;
 #define WADNAMECHECK(name) (!strncmp(name, "WADNAME", 7))