diff --git a/src/am_map.cpp b/src/am_map.cpp
index 28739c8561..62af8ed672 100644
--- a/src/am_map.cpp
+++ b/src/am_map.cpp
@@ -177,6 +177,45 @@ CVAR (Color, am_ovthingcolor_friend,	0xe88800,	CVAR_ARCHIVE);
 CVAR (Color, am_ovthingcolor_monster,	0xe88800,	CVAR_ARCHIVE);
 CVAR (Color, am_ovthingcolor_item,		0xe88800,	CVAR_ARCHIVE);
 
+// Disable the ML_DONTDRAW line flag if x% of all lines in a map are flagged with it
+// (To counter annoying mappers who think they are smart by making the automap unusable)
+bool am_showallenabled;
+
+CUSTOM_CVAR (Int, am_showalllines, -1, 0)	// This is a cheat so don't save it.
+{
+	int flagged = 0;
+	int total = 0;
+	if (self > 0)
+	{
+		for(int i=0;i<numlines;i++)
+		{
+			line_t *line = &lines[i];
+
+			// disregard intra-sector lines
+			if (line->frontsector == line->backsector) continue;	
+
+			// disregard control sectors for deep water
+			if (line->frontsector->e->FakeFloor.Sectors.Size() > 0) continue;	
+
+			// disregard control sectors for 3D-floors
+			if (line->frontsector->e->XFloor.attached.Size() > 0) continue;	
+
+			total++;
+			if (line->flags & ML_DONTDRAW) flagged++;
+		}
+		am_showallenabled =  (flagged * 100 / total >= self);
+	}
+	else if (self == 0)
+	{
+		am_showallenabled = true;
+	}
+	else
+	{
+		am_showallenabled = false;
+	}
+}
+
+
 // drawing stuff
 #define AM_PANDOWNKEY	KEY_DOWNARROW
 #define AM_PANUPKEY		KEY_UPARROW
@@ -946,6 +985,8 @@ void AM_LevelInit ()
 	if (scale_mtof > max_scale_mtof)
 		scale_mtof = min_scale_mtof;
 	scale_ftom = MapDiv(MAPUNIT, scale_mtof);
+
+	am_showalllines.Callback();
 }
 
 //=============================================================================
@@ -1601,7 +1642,12 @@ void AM_drawWalls (bool allmap)
 		if (am_cheat != 0 || (lines[i].flags & ML_MAPPED))
 		{
 			if ((lines[i].flags & ML_DONTDRAW) && am_cheat == 0)
-				continue;
+			{
+				if (!am_showallenabled || CheckCheatmode(false))
+				{
+					continue;
+				}
+			}
 
 			if (AM_CheckSecret(&lines[i]))
 			{
@@ -1680,8 +1726,14 @@ void AM_drawWalls (bool allmap)
 		}
 		else if (allmap)
 		{
-			if (!(lines[i].flags & ML_DONTDRAW))
-				AM_drawMline(&l, NotSeenColor);
+			if ((lines[i].flags & ML_DONTDRAW) && am_cheat == 0)
+			{
+				if (!am_showallenabled || CheckCheatmode(false))
+				{
+					continue;
+				}
+			}
+			AM_drawMline(&l, NotSeenColor);
 		}
     }
 }
diff --git a/src/b_bot.cpp b/src/b_bot.cpp
index 3911264cd6..cee4086ae1 100644
--- a/src/b_bot.cpp
+++ b/src/b_bot.cpp
@@ -67,8 +67,6 @@ CCMD (removebots)
 	Net_WriteByte (DEM_KILLBOTS);
 }
 
-extern bool CheckCheatmode ();
-
 CCMD (freeze)
 {
 	if (CheckCheatmode ())
diff --git a/src/c_cmds.cpp b/src/c_cmds.cpp
index 0567427cf5..6d21a79225 100644
--- a/src/c_cmds.cpp
+++ b/src/c_cmds.cpp
@@ -80,11 +80,11 @@ CCMD (toggleconsole)
 	C_ToggleConsole();
 }
 
-bool CheckCheatmode ()
+bool CheckCheatmode (bool printmsg)
 {
 	if ((G_SkillProperty(SKILLP_DisableCheats) || netgame || deathmatch) && (!sv_cheats))
 	{
-		Printf ("sv_cheats must be true to enable this command.\n");
+		if (printmsg) Printf ("sv_cheats must be true to enable this command.\n");
 		return true;
 	}
 	else
diff --git a/src/c_dispatch.h b/src/c_dispatch.h
index fb76f1aee0..a19352d32b 100644
--- a/src/c_dispatch.h
+++ b/src/c_dispatch.h
@@ -39,6 +39,8 @@
 class FConfigFile;
 class APlayerPawn;
 
+extern bool CheckCheatmode (bool printmsg = true);
+
 void C_ExecCmdLineParams ();
 
 // Add commands to the console as if they were typed in. Can handle wait
diff --git a/src/d_main.cpp b/src/d_main.cpp
index 61e76da0d3..65973e3c87 100644
--- a/src/d_main.cpp
+++ b/src/d_main.cpp
@@ -120,7 +120,6 @@ extern void M_SetDefaultMode ();
 extern void R_ExecuteSetViewSize ();
 extern void G_NewInit ();
 extern void SetupPlayerClasses ();
-extern bool CheckCheatmode ();
 const IWADInfo *D_FindIWAD(TArray<FString> &wadfiles, const char *iwad, const char *basewad);
 
 // PUBLIC FUNCTION PROTOTYPES ----------------------------------------------
diff --git a/src/info.cpp b/src/info.cpp
index 62556b1e99..1b49ce7ddb 100644
--- a/src/info.cpp
+++ b/src/info.cpp
@@ -454,7 +454,6 @@ CCMD (dumpmapthings)
 	FDoomEdMap::DumpMapThings ();
 }
 
-bool CheckCheatmode ();
 
 static void SummonActor (int command, int command2, FCommandLine argv)
 {
diff --git a/src/m_cheat.cpp b/src/m_cheat.cpp
index a79ca3ad7e..45175c50ac 100644
--- a/src/m_cheat.cpp
+++ b/src/m_cheat.cpp
@@ -1062,7 +1062,6 @@ void cht_Suicide (player_t *plyr)
 	}
 }
 
-bool CheckCheatmode ();
 
 CCMD (mdk)
 {
diff --git a/src/p_interaction.cpp b/src/p_interaction.cpp
index 6cdf86ab5d..7dfd7398f3 100644
--- a/src/p_interaction.cpp
+++ b/src/p_interaction.cpp
@@ -1539,7 +1539,6 @@ void P_PoisonDamage (player_t *player, AActor *source, int damage,
 	return;
 }
 
-bool CheckCheatmode ();
 
 CCMD (kill)
 {
diff --git a/src/st_stuff.cpp b/src/st_stuff.cpp
index 59b65ef85a..08e6f0be4c 100644
--- a/src/st_stuff.cpp
+++ b/src/st_stuff.cpp
@@ -293,7 +293,6 @@ static cheatseq_t SpecialCheats[] =
 };
 
 
-extern bool CheckCheatmode ();
 
 CVAR(Bool, allcheats, false, CVAR_ARCHIVE)