diff --git a/specs/udmf_zdoom.txt b/specs/udmf_zdoom.txt
index 6c2fde912..51329bad5 100644
--- a/specs/udmf_zdoom.txt
+++ b/specs/udmf_zdoom.txt
@@ -112,6 +112,7 @@ Note: All <bool> fields default to false unless mentioned otherwise.
       checkswitchrange = <bool>;// Switches can only be activated when vertically reachable.
       blockprojectiles = <bool>;// Line blocks all projectiles
       blockuse = <bool>;		// Line blocks all use actions
+      blocksight = <bool>;		// Line blocks monster line of sight
                     
    }
    
@@ -162,8 +163,8 @@ Note: All <bool> fields default to false unless mentioned otherwise.
       alphafloor = <float>;           // translucency of floor plane (only has meaning with Sector_SetPortal) Default is 1.0.
       alphaceiling = <float>;         // translucency of ceiling plane (only has meaning with Sector_SetPortal) Default is 1.0.
       gravity = <float>;              // Sector's gravity. Default is 1.0.
-      lightcolor = <integer>;         // Sector'S light color as RRGGBB value, default = 0xffffff.
-      fadecolor = <integer>;          // Sector'S fog color as RRGGBB value, default = 0x000000.
+      lightcolor = <integer>;         // Sector's light color as RRGGBB value, default = 0xffffff.
+      fadecolor = <integer>;          // Sector's fog color as RRGGBB value, default = 0x000000.
       desaturation = <float>;         // Color desaturation factor. 0 = none, 1 = full, default = 0.
       silent = <bool>;                // Actors in this sector make no sound,
       nofallingdamage = <bool>;		  // Falling damage is disabled in this sector
@@ -183,12 +184,8 @@ Note: All <bool> fields default to false unless mentioned otherwise.
    
    thing
    {
-      skill# = <bool>			// Unlike the base spec, # can range from 1-8.
-                                // 8 is the maximum amount of skills the skill 
-                                // menu can display.
-      class# = <bool>			// Unlike the base spec, # can range from 1-8.
-                                // 8 is the maximum amount of classes the class
-                                // menu can display.
+      skill# = <bool>			// Unlike the base spec, # can range from 1-16.
+      class# = <bool>			// Unlike the base spec, # can range from 1-16.
 	  conversation = <int>		// Assigns a conversation dialogue to this thing.
 								// Parameter is the conversation ID, 0 meaning none.
 	  countsecret = <bool>;     // Picking up this actor counts as a secret.
@@ -292,6 +289,10 @@ Added 'countsecret' actor property.
 1.15 14.12.2010
 Added vertex floor and ceiling height properties
 
+1.16 23.01.2011
+Added blocksight linedef flag
+Removed remarks of 8 being the maximum number of player classes/skill levels the menu can handle so the spec now properly lists 16 as limit.
+
 ===============================================================================
 EOF
 ===============================================================================
diff --git a/src/actionspecials.h b/src/actionspecials.h
index 8fcb3cf8d..0751621fb 100644
--- a/src/actionspecials.h
+++ b/src/actionspecials.h
@@ -227,7 +227,7 @@ DEFINE_SPECIAL(Elevator_LowerToNearest, 247, 2, 2, 2)
 DEFINE_SPECIAL(HealThing, 248, 1, 2, 2)
 DEFINE_SPECIAL(Door_CloseWaitOpen, 249, 3, 4, 4)
 DEFINE_SPECIAL(Floor_Donut, 250, 3, 3, 3)
-DEFINE_SPECIAL(FloorAndCeiling_LowerRaise, 251, 3, 3, 3)
+DEFINE_SPECIAL(FloorAndCeiling_LowerRaise, 251, 3, 3, 4)
 DEFINE_SPECIAL(Ceiling_RaiseToNearest, 252, 2, 2, 2)
 DEFINE_SPECIAL(Ceiling_LowerToLowest, 253, 2, 2, 2)
 DEFINE_SPECIAL(Ceiling_LowerToFloor, 254, 2, 2, 2)
diff --git a/src/doomdata.h b/src/doomdata.h
index 83345a671..64ac86e5e 100644
--- a/src/doomdata.h
+++ b/src/doomdata.h
@@ -152,6 +152,7 @@ enum ELineFlags
 	ML_FIRSTSIDEONLY			= 0x00800000,	// activated only when crossed from front side
 	ML_BLOCKPROJECTILE			= 0x01000000,
 	ML_BLOCKUSE					= 0x02000000,	// blocks all use actions through this line
+	ML_BLOCKSIGHT				= 0x04000000,	// blocks monster line of sight
 };
 
 
diff --git a/src/namedef.h b/src/namedef.h
index 52fc87e66..2a3bc3cf2 100644
--- a/src/namedef.h
+++ b/src/namedef.h
@@ -443,6 +443,7 @@ xx(smoothlighting)
 xx(blockprojectiles)
 xx(blockuse)
 xx(hidden)
+xx(blocksight)
 
 xx(Renderstyle)
 
diff --git a/src/p_lnspec.cpp b/src/p_lnspec.cpp
index 1b3f627a4..88801733f 100644
--- a/src/p_lnspec.cpp
+++ b/src/p_lnspec.cpp
@@ -2473,6 +2473,7 @@ FUNC(LS_Line_SetBlocking)
 		ML_BLOCKEVERYTHING,
 		ML_RAILING,
 		ML_BLOCKUSE,
+		ML_BLOCKSIGHT,
 		-1
 	};
 
diff --git a/src/p_sight.cpp b/src/p_sight.cpp
index 359b5d4d3..3e699cab1 100644
--- a/src/p_sight.cpp
+++ b/src/p_sight.cpp
@@ -256,7 +256,7 @@ bool SightCheck::P_SightCheckLine (line_t *ld)
 	}
 
 	// try to early out the check
-	if (!ld->backsector || !(ld->flags & ML_TWOSIDED))
+	if (!ld->backsector || !(ld->flags & ML_TWOSIDED) || (ld->flags & ML_BLOCKSIGHT))
 		return false;	// stop checking
 
 	// [RH] don't see past block everything lines
diff --git a/src/p_udmf.cpp b/src/p_udmf.cpp
index 72c3cb24c..1215d0839 100644
--- a/src/p_udmf.cpp
+++ b/src/p_udmf.cpp
@@ -874,6 +874,10 @@ public:
 				Flag(ld->flags, ML_BLOCKUSE, key); 
 				continue;
 
+			case NAME_blocksight:
+				Flag(ld->flags, ML_BLOCKSIGHT, key); 
+				continue;
+
 			default:
 				break;
 			}