diff --git a/src/doomdata.h b/src/doomdata.h
index 028ae55121..8592462611 100644
--- a/src/doomdata.h
+++ b/src/doomdata.h
@@ -139,7 +139,7 @@ enum ELineFlags
 	ML_ADDTRANS					= 0x00000400,	// additive translucency (can only be set internally)
 
 	// Extended flags
-	ML_MONSTERSCANACTIVATE		= 0x00002000,	// [RH] Monsters (as well as players) can active the line
+	ML_MONSTERSCANACTIVATE		= 0x00002000,	// [RH] Monsters (as well as players) can activate the line
 	ML_BLOCK_PLAYERS			= 0x00004000,
 	ML_BLOCKEVERYTHING			= 0x00008000,	// [RH] Line blocks everything
 	ML_ZONEBOUNDARY				= 0x00010000,
diff --git a/src/p_doors.cpp b/src/p_doors.cpp
index 29ec1fc6b3..ccfd61c5d5 100644
--- a/src/p_doors.cpp
+++ b/src/p_doors.cpp
@@ -626,6 +626,17 @@ void DAnimatedDoor::Tick ()
 				MoveCeiling (2048*FRACUNIT, m_BotDist, -1);
 				m_Sector->ceilingdata = NULL;
 				Destroy ();
+				// Unset blocking flags on lines that didn't start with them. Since the
+				// ceiling is down now, we shouldn't need this flag anymore to keep things
+				// from getting through.
+				if (!m_SetBlocking1)
+				{
+					m_Line1->flags &= ~ML_BLOCKING;
+				}
+				if (!m_SetBlocking2)
+				{
+					m_Line2->flags &= ~ML_BLOCKING;
+				}
 				break;
 			}
 			else
@@ -668,6 +679,14 @@ void DAnimatedDoor::Serialize (FArchive &arc)
 		<< m_Speed
 		<< m_Delay
 		<< basetex;
+	if (SaveVersion < 2336)
+	{
+		m_SetBlocking1 = m_SetBlocking2 = true;
+	}
+	else
+	{
+		arc << m_SetBlocking1 << m_SetBlocking2;
+	}
 
 	if (arc.IsLoading())
 	{
@@ -727,6 +746,8 @@ DAnimatedDoor::DAnimatedDoor (sector_t *sec, line_t *line, int speed, int delay)
 	m_Delay = delay;
 	m_Timer = m_Speed;
 	m_Frame = 0;
+	m_SetBlocking1 = !!(m_Line1->flags & ML_BLOCKING);
+	m_SetBlocking2 = !!(m_Line2->flags & ML_BLOCKING);
 	m_Line1->flags |= ML_BLOCKING;
 	m_Line2->flags |= ML_BLOCKING;
 	m_BotDist = m_Sector->ceilingplane.d;
diff --git a/src/p_map.cpp b/src/p_map.cpp
index 9ff863e2b0..09d1f944af 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -620,16 +620,17 @@ bool PIT_CheckLine (line_t *ld, const FBoundingBox &box, FCheckPosition &tm)
 		return false;
 	}
 
-		// MBF bouncers are treated as missiles here.
-		bool Projectile = (tm.thing->flags & MF_MISSILE || tm.thing->BounceFlags & BOUNCE_MBF);
-		// MBF considers that friendly monsters are not blocked by monster-blocking lines.
-		// This is added here as a compatibility option. Note that monsters that are dehacked
-		// into being friendly with the MBF flag automatically gain MF3_NOBLOCKMONST, so this
-		// just optionally generalizes the behavior to other friendly monsters.
-		bool NotBlocked = ((tm.thing->flags3 & MF3_NOBLOCKMONST)
-			|| ((i_compatflags & COMPATF_NOBLOCKFRIENDS) && (tm.thing->flags & MF_FRIENDLY)));
+	// MBF bouncers are treated as missiles here.
+	bool Projectile = (tm.thing->flags & MF_MISSILE || tm.thing->BounceFlags & BOUNCE_MBF);
+	// MBF considers that friendly monsters are not blocked by monster-blocking lines.
+	// This is added here as a compatibility option. Note that monsters that are dehacked
+	// into being friendly with the MBF flag automatically gain MF3_NOBLOCKMONST, so this
+	// just optionally generalizes the behavior to other friendly monsters.
+	bool NotBlocked = ((tm.thing->flags3 & MF3_NOBLOCKMONST)
+		|| ((i_compatflags & COMPATF_NOBLOCKFRIENDS) && (tm.thing->flags & MF_FRIENDLY)));
 
-		if (!(Projectile) || (ld->flags & (ML_BLOCKEVERYTHING|ML_BLOCKPROJECTILE)))	{
+	if (!(Projectile) || (ld->flags & (ML_BLOCKEVERYTHING|ML_BLOCKPROJECTILE)))
+	{
 		if (ld->flags & ML_RAILING)
 		{
 			rail = true;
diff --git a/src/p_spec.h b/src/p_spec.h
index ca0d9492c5..ca3694c098 100644
--- a/src/p_spec.h
+++ b/src/p_spec.h
@@ -640,6 +640,7 @@ protected:
 	};
 	int m_Speed;
 	int m_Delay;
+	bool m_SetBlocking1, m_SetBlocking2;
 
 	friend bool EV_SlidingDoor (line_t *line, AActor *thing, int tag, int speed, int delay);
 private: