diff --git a/src/d_main.c b/src/d_main.c
index 9652f0d10..fd05bc3cd 100644
--- a/src/d_main.c
+++ b/src/d_main.c
@@ -1514,7 +1514,8 @@ void D_SRB2Main(void)
 	//
 	// search for mainwad maps
 	//
-	P_InitMapData(false);
+	P_InitMapData();
+	basenummapheaders = nummapheaders;
 
 	CON_SetLoadingProgress(LOADED_IWAD);
 
@@ -1525,7 +1526,7 @@ void D_SRB2Main(void)
 	//
 	// search for pwad maps
 	//
-	P_InitMapData(true);
+	P_InitMapData();
 
 	CON_SetLoadingProgress(LOADED_PWAD);
 
diff --git a/src/dehacked.c b/src/dehacked.c
index 6d44b87fb..66567fb05 100644
--- a/src/dehacked.c
+++ b/src/dehacked.c
@@ -605,7 +605,10 @@ static void DEH_LoadDehackedFile(MYFILE *f, boolean mainfile)
 	} // end while
 
 	if (gamedataadded)
+	{
+		basenummapheaders = nummapheaders;
 		G_LoadGameData();
+	}
 
 	if (gamestate == GS_MENU || gamestate == GS_TITLESCREEN)
 	{
diff --git a/src/doomstat.h b/src/doomstat.h
index 7d14f1d5a..26ea96cdb 100644
--- a/src/doomstat.h
+++ b/src/doomstat.h
@@ -551,7 +551,7 @@ struct mapheader_t
 #define LF2_FINISHNEEDED	(1<<3) ///< Not available in Time Attack modes until you beat the level
 
 extern mapheader_t** mapheaderinfo;
-extern INT32 nummapheaders, mapallocsize;
+extern INT32 nummapheaders, basenummapheaders, mapallocsize;
 
 struct unloaded_mapheader_t
 {
diff --git a/src/g_game.c b/src/g_game.c
index 17d16b47a..36de12b56 100644
--- a/src/g_game.c
+++ b/src/g_game.c
@@ -193,6 +193,7 @@ quake_t *g_quakes = NULL;
 // Map Header Information
 mapheader_t** mapheaderinfo = {NULL};
 INT32 nummapheaders = 0;
+INT32 basenummapheaders = 0;
 INT32 mapallocsize = 0;
 
 unloaded_mapheader_t *unloadedmapheaders = NULL;
diff --git a/src/p_inter.c b/src/p_inter.c
index 2b9542295..0d99598dc 100644
--- a/src/p_inter.c
+++ b/src/p_inter.c
@@ -642,6 +642,7 @@ void P_TouchSpecialThing(mobj_t *special, mobj_t *toucher, boolean heightcheck)
 					return;
 				}
 
+				// See also P_SprayCanInit
 				UINT16 can_id = mapheaderinfo[gamemap-1]->cache_spraycan;
 
 				if (can_id < gamedata->numspraycans)
@@ -649,7 +650,8 @@ void P_TouchSpecialThing(mobj_t *special, mobj_t *toucher, boolean heightcheck)
 					// Assigned to this level, has been grabbed
 					return;
 				}
-				//else
+				// Prevent footguns - these won't persist when custom levels are unloaded
+				else if (gamemap-1 < basenummapheaders)
 				{
 					// Unassigned, get the next grabbable colour
 					can_id = gamedata->gotspraycans;
diff --git a/src/p_mobj.c b/src/p_mobj.c
index d4823700c..76ae716a3 100644
--- a/src/p_mobj.c
+++ b/src/p_mobj.c
@@ -12437,6 +12437,7 @@ static boolean P_SetupEmblem(mapthing_t *mthing, mobj_t *mobj)
 
 void P_SprayCanInit(mobj_t* mobj)
 {
+	// See also P_TouchSpecialThing
 	UINT16 can_id = mapheaderinfo[gamemap-1]->cache_spraycan;
 
 	if (can_id < gamedata->numspraycans)
@@ -12444,7 +12445,8 @@ void P_SprayCanInit(mobj_t* mobj)
 		// Assigned to this level, has been grabbed
 		mobj->renderflags = (tr_trans50 << RF_TRANSSHIFT);
 	}
-	else
+	// Prevent footguns - these won't persist when custom levels are unloaded
+	else if (gamemap-1 < basenummapheaders)
 	{
 		// Unassigned, get the next grabbable colour
 		can_id = gamedata->gotspraycans;
diff --git a/src/p_setup.c b/src/p_setup.c
index f5461fa35..f55c13b09 100644
--- a/src/p_setup.c
+++ b/src/p_setup.c
@@ -8564,7 +8564,7 @@ lumpnum_t wadnamelump = LUMPERROR;
 INT16 wadnamemap = 0; // gamemap based
 
 // Initialising map data (and catching replacements)...
-UINT8 P_InitMapData(boolean existingmapheaders)
+UINT8 P_InitMapData(void)
 {
 	UINT8 ret = 0;
 	INT32 i, j;
@@ -8616,7 +8616,7 @@ UINT8 P_InitMapData(boolean existingmapheaders)
 		if (maplump == LUMPERROR)
 		{
 #ifndef DEVELOP
-			if (!existingmapheaders)
+			if (!basenummapheaders)
 			{
 				I_Error("P_InitMapData: Base map %s has a header but no level\n", name);
 			}
@@ -8633,7 +8633,7 @@ UINT8 P_InitMapData(boolean existingmapheaders)
 			ret |= MAPRET_ADDED;
 			CONS_Printf("%s\n", name);
 
-			if (existingmapheaders && mapheaderinfo[i]->lumpnum != LUMPERROR)
+			if (basenummapheaders && mapheaderinfo[i]->lumpnum != LUMPERROR)
 			{
 				G_SetGameModified(multiplayer, true); // oops, double-defined - no record attack privileges for you
 
@@ -8950,7 +8950,7 @@ boolean P_MultiSetupWadFiles(boolean fullsetup)
 
 	if (partadd_stage == 2)
 	{
-		UINT8 mapsadded = P_InitMapData(true);
+		UINT8 mapsadded = P_InitMapData();
 
 		if (!mapsadded)
 			CONS_Printf(M_GetText("No maps added\n"));
diff --git a/src/p_setup.h b/src/p_setup.h
index 1d474dd10..bcffd85b2 100644
--- a/src/p_setup.h
+++ b/src/p_setup.h
@@ -114,7 +114,7 @@ boolean P_AddWadFile(const char *wadfilename);
 
 #define MAPRET_ADDED (1)
 #define MAPRET_CURRENTREPLACED (1<<1)
-UINT8 P_InitMapData(boolean existingmapheaders);
+UINT8 P_InitMapData(void);
 extern lumpnum_t wadnamelump;
 extern INT16 wadnamemap;
 #define WADNAMECHECK(name) (!strncmp(name, "WADNAME", 7))