diff --git a/docs/rh-log.txt b/docs/rh-log.txt
index 82ecd2a47a..d9dc532fcf 100644
--- a/docs/rh-log.txt
+++ b/docs/rh-log.txt
@@ -1,3 +1,7 @@
+July 11, 2006 (Changes by Graf Zahl)
+- Changed the additive scrollers option into a compatibility flag so that it can
+  be changed from the menu.
+
 July 10, 2006
 - Fixed closed doors between the front sector's floor and ceiling the right way.
   I was just missing a non-null texture check.
diff --git a/src/d_main.cpp b/src/d_main.cpp
index a3d83ea5e7..21ae355ad0 100644
--- a/src/d_main.cpp
+++ b/src/d_main.cpp
@@ -396,6 +396,7 @@ CVAR (Flag, compat_soundtarget,	compatflags, COMPATF_SOUNDTARGET);
 CVAR (Flag, compat_dehhealth,	compatflags, COMPATF_DEHHEALTH);
 CVAR (Flag, compat_trace,		compatflags, COMPATF_TRACE);
 CVAR (Flag, compat_dropoff,		compatflags, COMPATF_DROPOFF);
+CVAR (Flag, compat_boomscroll,	compatflags, COMPATF_BOOMSCROLL);
 
 //==========================================================================
 //
diff --git a/src/doomdef.h b/src/doomdef.h
index 2d2e19f108..fdb174ed0e 100644
--- a/src/doomdef.h
+++ b/src/doomdef.h
@@ -274,6 +274,7 @@ enum
 	COMPATF_DEHHEALTH		= 1 << 12,	// Limit deh.MaxHealth to the health bonus (as in Doom2.exe)
 	COMPATF_TRACE			= 1 << 13,	// Trace ignores lines with the same sector on both sides
 	COMPATF_DROPOFF			= 1 << 14,	// Monsters cannot move when hanging over a dropoff
+	COMPATF_BOOMSCROLL		= 1 << 15,	// Scrolling sectors are additive like in Boom
 };
 
 // phares 3/20/98:
diff --git a/src/g_level.cpp b/src/g_level.cpp
index 86e99edfe2..68242e781d 100644
--- a/src/g_level.cpp
+++ b/src/g_level.cpp
@@ -259,7 +259,8 @@ static const char *MapInfoMapLevel[] =
 	"compat_soundtarget",	
 	"compat_dehhealth",	
 	"compat_trace",		
-	"compat_dropoff",		
+	"compat_dropoff",
+	"compat_boomscroll",
 
 	NULL
 };
@@ -359,7 +360,7 @@ MapHandlers[] =
 	{ MITYPE_REDIRECT,	lioffset(RedirectMap), 0 },
 	{ MITYPE_CLRFLAG,	LEVEL_LAXMONSTERACTIVATION, LEVEL_LAXACTIVATIONMAPINFO },
 	{ MITYPE_SETFLAG,	LEVEL_LAXMONSTERACTIVATION, LEVEL_LAXACTIVATIONMAPINFO },
-	{ MITYPE_SETFLAG,	LEVEL_ADDITIVE_SCROLLERS, 0 },
+	{ MITYPE_COMPATFLAG, COMPATF_BOOMSCROLL},
 	{ MITYPE_SETFLAG,	LEVEL_CAVERNS_OF_DARKNESS, 0 },
 	{ MITYPE_LUMPNAME,	lioffset(exitpic), 0 },
 	{ MITYPE_LUMPNAME,	lioffset(exitpic), 0 },
@@ -390,6 +391,7 @@ MapHandlers[] =
 	{ MITYPE_COMPATFLAG, COMPATF_DEHHEALTH},
 	{ MITYPE_COMPATFLAG, COMPATF_TRACE},
 	{ MITYPE_COMPATFLAG, COMPATF_DROPOFF},
+	{ MITYPE_COMPATFLAG, COMPATF_BOOMSCROLL},
 };
 
 static const char *MapInfoClusterLevel[] =
@@ -1000,7 +1002,8 @@ static void ParseMapInfoLower (MapInfoHandler *handlers,
 			break;
 
 		case MITYPE_COMPATFLAG:
-			SC_MustGetNumber();
+			if (!SC_CheckNumber()) sc_Number = 1;
+
 			if (levelinfo != NULL)
 			{
 				if (sc_Number) levelinfo->compatflags |= (DWORD)handler->data1;
diff --git a/src/g_level.h b/src/g_level.h
index 945dc04ce6..b73c064ab6 100644
--- a/src/g_level.h
+++ b/src/g_level.h
@@ -93,20 +93,19 @@
 #define LEVEL_LAXMONSTERACTIVATION	UCONST64(0x400000000)		// Monsters can open doors depending on the door speed
 #define LEVEL_LAXACTIVATIONMAPINFO	UCONST64(0x800000000)		// LEVEL_LAXMONSTERACTIVATION is not a default.
 
-#define LEVEL_ADDITIVE_SCROLLERS	UCONST64(0x1000000000)		// scrollers add their momentum instead of averaging it
-#define LEVEL_CAVERNS_OF_DARKNESS	UCONST64(0x2000000000)		// to translate the special sector types of CoD.
+#define LEVEL_CAVERNS_OF_DARKNESS	UCONST64(0x1000000000)		// to translate the special sector types of CoD.
 
-#define LEVEL_KEEPFULLINVENTORY		UCONST64(0x4000000000)		// doesn't reduce the amount of inventory items to 1
+#define LEVEL_KEEPFULLINVENTORY		UCONST64(0x2000000000)		// doesn't reduce the amount of inventory items to 1
 
-#define LEVEL_MUSICDEFINED			UCONST64(0x8000000000)		// a marker to disable the $map command in SNDINFO for this map
-#define LEVEL_MONSTERFALLINGDAMAGE	UCONST64(0x10000000000)
-#define LEVEL_CLIPMIDTEX			UCONST64(0x20000000000)
-#define LEVEL_WRAPMIDTEX			UCONST64(0x40000000000)
+#define LEVEL_MUSICDEFINED			UCONST64(0x4000000000)		// a marker to disable the $map command in SNDINFO for this map
+#define LEVEL_MONSTERFALLINGDAMAGE	UCONST64(0x8000000000)
+#define LEVEL_CLIPMIDTEX			UCONST64(0x10000000000)
+#define LEVEL_WRAPMIDTEX			UCONST64(0x20000000000)
 
-#define LEVEL_CROUCH_NO				UCONST64(0x80000000000)
-#define LEVEL_CROUCH_YES			UCONST64(0x100000000000)
+#define LEVEL_CROUCH_NO				UCONST64(0x40000000000)
+#define LEVEL_CROUCH_YES			UCONST64(0x80000000000)
 
-#define LEVEL_PAUSE_MUSIC_IN_MENUS	UCONST64(0x200000000000)
+#define LEVEL_PAUSE_MUSIC_IN_MENUS	UCONST64(0x100000000000)
 
 struct acsdefered_s;
 
diff --git a/src/m_options.cpp b/src/m_options.cpp
index d46b3fc9fc..68f1562e14 100644
--- a/src/m_options.cpp
+++ b/src/m_options.cpp
@@ -987,6 +987,7 @@ static menuitem_t CompatibilityItems[] = {
 	{ bitflag,	"DEH health settings like Doom2.exe",		{&compatflags}, {0}, {0}, {0}, {(value_t *)COMPATF_DEHHEALTH} },
 	{ bitflag,	"Self ref. sectors don't block shots",		{&compatflags}, {0}, {0}, {0}, {(value_t *)COMPATF_TRACE} },
 	{ bitflag,	"Monsters get stuck over dropoffs",			{&compatflags}, {0}, {0}, {0}, {(value_t *)COMPATF_DROPOFF} },
+	{ bitflag,	"Boom scrollers are additive",				{&compatflags}, {0}, {0}, {0}, {(value_t *)COMPATF_BOOMSCROLL} },
 	
 	{ discrete, "Interpolate monster movement",	{&nomonsterinterpolation},		{2.0}, {0.0},	{0.0}, {NoYes} },
 };
diff --git a/src/p_mobj.cpp b/src/p_mobj.cpp
index 70c1c3b84f..2c5f631c44 100644
--- a/src/p_mobj.cpp
+++ b/src/p_mobj.cpp
@@ -2703,7 +2703,7 @@ void AActor::Tick ()
 		// Some levels designed with Boom in mind actually want things to accelerate
 		// at neighboring scrolling sector boundaries. But it is only important for
 		// non-player objects.
-		if (player != NULL || !(level.flags & LEVEL_ADDITIVE_SCROLLERS))
+		if (player != NULL || !(i_compatflags & COMPATF_BOOMSCROLL))
 		{
 			if (countx > 1)
 			{