diff --git a/docs/rh-log.txt b/docs/rh-log.txt
index e234fee0f0..661718eb4c 100644
--- a/docs/rh-log.txt
+++ b/docs/rh-log.txt
@@ -1,4 +1,5 @@
 May 31, 2009  (Changes by Graf Zahl)
+- Added Gez's THRUSPECIES submission.
 - Added loading directories into the lump directory.
 - fixed: The Dehacked parser could not parse flag values with the highest bit
   set because it used atoi to convert the string into a number.
diff --git a/src/actor.h b/src/actor.h
index 6069539e79..1b144a56ca 100644
--- a/src/actor.h
+++ b/src/actor.h
@@ -305,6 +305,8 @@ enum
 	MF5_MOVEWITHSECTOR	= 0x80000000,	// P_ChangeSector() will still process this actor if it has MF_NOBLOCKMAP
 
 	MF6_NOBOSSRIP		= 0x00000001,	// For rippermissiles: Don't rip through bosses.
+	MF6_THRUSPECIES		= 0x00000002,	// Actors passes through other of the same species.
+	MF6_MTHRUSPECIES	= 0x00000004,	// Missile passes through actors of its shooter's species.
 
 
 // --- mobj.renderflags ---
diff --git a/src/p_map.cpp b/src/p_map.cpp
index 3669d61f02..703e8ab4a4 100644
--- a/src/p_map.cpp
+++ b/src/p_map.cpp
@@ -755,6 +755,9 @@ bool PIT_CheckThing (AActor *thing, FCheckPosition &tm)
 	if ((thing->flags2 | tm.thing->flags2) & MF2_THRUACTORS) 
 		return true;
 
+	if ((tm.thing->flags6 & MF6_THRUSPECIES) && (tm.thing->Species == thing->Species))
+		return true;
+
 	if (!(thing->flags & (MF_SOLID|MF_SPECIAL|MF_SHOOTABLE)) )
 		return true;	// can't hit thing
 
@@ -836,6 +839,12 @@ bool PIT_CheckThing (AActor *thing, FCheckPosition &tm)
 		{
 			return true;
 		}
+
+		if ((tm.thing->flags6 & MF6_MTHRUSPECIES) 
+			&& tm.thing->target // NULL pointer check
+			&& (tm.thing->target->GetSpecies() == thing->GetSpecies()))
+			return true;
+
 		// Check for rippers passing through corpses
 		if ((thing->flags & MF_CORPSE) && (tm.thing->flags2 & MF2_RIP) && !(thing->flags & MF_SHOOTABLE))
 		{
diff --git a/src/p_mobj.cpp b/src/p_mobj.cpp
index 9eb2286de2..941b0a1a75 100644
--- a/src/p_mobj.cpp
+++ b/src/p_mobj.cpp
@@ -5118,7 +5118,7 @@ FName AActor::GetSpecies()
 				break;
 		}
 	}
-	return thistype->TypeName;
+	return Species = thistype->TypeName; // [GZ] Speeds up future calls.
 }
 
 //==========================================================================
diff --git a/src/thingdef/thingdef_data.cpp b/src/thingdef/thingdef_data.cpp
index c6b03fee4c..c1d91d618b 100644
--- a/src/thingdef/thingdef_data.cpp
+++ b/src/thingdef/thingdef_data.cpp
@@ -210,6 +210,8 @@ static FFlagDef ActorFlags[]=
 	DEFINE_FLAG(MF5, MOVEWITHSECTOR, AActor, flags5),
 
 	DEFINE_FLAG(MF6, NOBOSSRIP, AActor, flags6),
+	DEFINE_FLAG(MF6, THRUSPECIES, AActor, flags6),
+	DEFINE_FLAG(MF6, MTHRUSPECIES, AActor, flags6),
 
 	// Effect flags
 	DEFINE_FLAG(FX, VISIBILITYPULSE, AActor, effects),