diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index a5164e84b6..395e72e2c1 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -844,7 +844,6 @@ set( NOT_COMPILED_SOURCE_FILES
 	g_doom/a_painelemental.cpp
 	g_doom/a_revenant.cpp
 	g_doom/a_scriptedmarine.cpp
-	g_doom/a_spidermaster.cpp
 	g_heretic/a_chicken.cpp
 	g_heretic/a_dsparil.cpp
 	g_heretic/a_hereticartifacts.cpp
diff --git a/src/g_doom/a_doommisc.cpp b/src/g_doom/a_doommisc.cpp
index 4c8be07f1e..df42bfa7be 100644
--- a/src/g_doom/a_doommisc.cpp
+++ b/src/g_doom/a_doommisc.cpp
@@ -30,7 +30,6 @@
 #include "a_lostsoul.cpp"
 #include "a_painelemental.cpp"
 #include "a_revenant.cpp"
-#include "a_spidermaster.cpp"
 #include "a_scriptedmarine.cpp"
 
 // The barrel of green goop ------------------------------------------------
diff --git a/src/g_doom/a_spidermaster.cpp b/src/g_doom/a_spidermaster.cpp
deleted file mode 100644
index 37d0deb184..0000000000
--- a/src/g_doom/a_spidermaster.cpp
+++ /dev/null
@@ -1,41 +0,0 @@
-/*
-#include "templates.h"
-#include "actor.h"
-#include "m_random.h"
-#include "s_sound.h"
-#include "p_local.h"
-#include "p_enemy.h"
-#include "a_action.h"
-#include "vm.h"
-*/
-
-static FRandom pr_spidrefire ("SpidRefire");
-
-DEFINE_ACTION_FUNCTION(AActor, A_SpidRefire)
-{
-	PARAM_SELF_PROLOGUE(AActor);
-
-	// keep firing unless target got out of sight
-	A_FaceTarget (self);
-
-	if (pr_spidrefire() < 10)
-		return 0;
-
-	if (!self->target
-		|| P_HitFriend (self)
-		|| self->target->health <= 0
-		|| !P_CheckSight (self, self->target, SF_SEEPASTBLOCKEVERYTHING|SF_SEEPASTSHOOTABLELINES))
-	{
-		self->SetState (self->SeeState);
-	}
-	return 0;
-}
-
-DEFINE_ACTION_FUNCTION(AActor, A_Metal)
-{
-	PARAM_SELF_PROLOGUE(AActor);
-
-	S_Sound (self, CHAN_BODY, "spider/walk", 1, ATTN_IDLE);
-	A_Chase (stack, self);
-	return 0;
-}
diff --git a/src/scripting/vm/vmexec.h b/src/scripting/vm/vmexec.h
index 2ddc505997..65891493e0 100644
--- a/src/scripting/vm/vmexec.h
+++ b/src/scripting/vm/vmexec.h
@@ -924,7 +924,7 @@ begin:
 		reg.d[a] = reg.d[B] ^ reg.d[C];
 		NEXTOP;
 	OP(XOR_RK):
-		ASSERTD(a); ASSERTD(B); ASSERTD(C);
+		ASSERTD(a); ASSERTD(B); ASSERTKD(C);
 		reg.d[a] = reg.d[B] ^ konstd[C];
 		NEXTOP;
 
diff --git a/wadsrc/static/zscript/actor.txt b/wadsrc/static/zscript/actor.txt
index 027aaf7dc9..02cb4f3cfc 100644
--- a/wadsrc/static/zscript/actor.txt
+++ b/wadsrc/static/zscript/actor.txt
@@ -113,8 +113,6 @@ class Actor : Thinker native
 	native void A_BossDeath();
 	native void A_SkullAttack(float speed = 20);
 	native void A_BetaSkullAttack();
-	native void A_Metal();
-	native void A_SpidRefire();
 	native void A_PainAttack(class<Actor> spawntype = "LostSoul", float angle = 0, int flags = 0, int limit = -1);
 	native void A_DualPainAttack(class<Actor> spawntype = "LostSoul");
 	native void A_PainDie(class<Actor> spawntype = "LostSoul");
diff --git a/wadsrc/static/zscript/doom/spidermaster.txt b/wadsrc/static/zscript/doom/spidermaster.txt
index b9f0600688..9a72a2bbe6 100644
--- a/wadsrc/static/zscript/doom/spidermaster.txt
+++ b/wadsrc/static/zscript/doom/spidermaster.txt
@@ -60,3 +60,34 @@ class SpiderMastermind : Actor
 		Stop;
 	}
 }
+
+//===========================================================================
+//
+// Code (must be attached to Actor)
+//
+//===========================================================================
+
+extend class Actor
+{
+	void A_SpidRefire()
+	{
+		// keep firing unless target got out of sight
+		A_FaceTarget();
+		if (Random[CPosRefire](0, 255) >= 10)
+		{
+			if (!target
+				|| HitFriend()
+				|| target.health <= 0
+				|| !CheckSight(target, SF_SEEPASTBLOCKEVERYTHING|SF_SEEPASTSHOOTABLELINES))
+			{
+				SetState(SeeState);
+			}
+		}
+	}
+
+	void A_Metal()
+	{
+		A_PlaySound("spider/walk", CHAN_BODY, 1, false, ATTN_IDLE);
+		A_Chase();
+	}
+}