diff --git a/artifacts/scripting/sfall function notes.txt b/artifacts/scripting/sfall function notes.txt
index aafe9127..dccfc845 100644
--- a/artifacts/scripting/sfall function notes.txt	
+++ b/artifacts/scripting/sfall function notes.txt	
@@ -473,10 +473,13 @@ Some utility/math functions are available:
 - clears the cache of FRM image files loaded into memory
 
 > int sfall_func1("set_unique_id", object)
-- assigns an unique ID number to the object and returns it. If an unique ID number has already been assigned to an object, then ID number is returned without reassignment
+> int sfall_func2("set_unique_id", object, int flag)
+- assigns a unique ID number to the object and returns it. If a unique ID number has already been assigned to an object, then ID number is returned without reassignment
+- items with unique IDs will not stack with other items of the same type in the inventory
 - to just get the current ID number of an object, use sfall_func2("get_object_data", object, OBJ_DATA_ID)
 - unique ID numbers are saved in your savegame, and have a range from 0x10000000 to 0x7FFFFFFF
-- there is also an unique ID number range for the player and party members from 18000 to 83535
+- there is also a unique ID number range for the player and party members from 18000 to 83535
+- to assign a new ID number generated by the engine to the object (i.e. unassign a unique ID), call the function with two arguments and pass -1 for the flag argument
 
 ------------------------
 ------ MORE INFO -------
diff --git a/sfall/Knockback.cpp b/sfall/Knockback.cpp
index 70e4ac97..546f665e 100644
--- a/sfall/Knockback.cpp
+++ b/sfall/Knockback.cpp
@@ -27,15 +27,9 @@
 
 static std::vector<long> NoBursts; // object id
 
-struct KnockbackModifier {
-	long id;
-	DWORD type;
-	double value;
-};
-
 static std::vector<KnockbackModifier> mTargets;
 static std::vector<KnockbackModifier> mAttackers;
-static std::vector<KnockbackModifier> mWeapons;
+std::vector<KnockbackModifier> Knockback_mWeapons;
 
 struct ChanceModifier {
 	long id;
@@ -73,7 +67,7 @@ static double ApplyModifiers(std::vector<KnockbackModifier>* mods, TGameObj* obj
 
 static DWORD __fastcall CalcKnockbackMod(int knockValue, int damage, TGameObj* weapon, TGameObj* attacker, TGameObj* target) {
 	double result = (double)damage / (double)knockValue;
-	result = ApplyModifiers(&mWeapons, weapon, result);
+	result = ApplyModifiers(&Knockback_mWeapons, weapon, result);
 	result = ApplyModifiers(&mAttackers, attacker, result);
 	result = ApplyModifiers(&mTargets, target, result);
 	return (DWORD)floor(result);
@@ -177,19 +171,25 @@ void _stdcall KnockbackSetMod(TGameObj* object, DWORD type, float val, DWORD on)
 	std::vector<KnockbackModifier>* mods;
 	switch (on) {
 	case 0:
-		mods = &mWeapons;
+		if (object->pid >> 24 != OBJ_TYPE_ITEM) return;
+		mods = &Knockback_mWeapons;
 		break;
 	case 1:
+		if (object->pid >> 24 != OBJ_TYPE_CRITTER) return;
 		mods = &mTargets;
 		break;
 	case 2:
+		if (object->pid >> 24 != OBJ_TYPE_CRITTER) return;
 		mods = &mAttackers;
 		break;
 	default:
 		return;
 	}
 
-	long id = SetObjectUniqueID(object);
+	long id = (on == 0)
+			? SetSpecialID(object)
+			: SetObjectUniqueID(object);
+
 	KnockbackModifier mod = { id, type, (double)val };
 	for (DWORD i = 0; i < mods->size(); i++) {
 		if ((*mods)[i].id == id) {
@@ -202,11 +202,9 @@ void _stdcall KnockbackSetMod(TGameObj* object, DWORD type, float val, DWORD on)
 
 void _stdcall KnockbackRemoveMod(TGameObj* object, DWORD on) {
 	std::vector<KnockbackModifier>* mods;
-	int id = object->ID;
 	switch (on) {
 	case 0:
-		object->ID = NewObjId(); // revert to engine range id
-		mods = &mWeapons;
+		mods = &Knockback_mWeapons;
 		break;
 	case 1:
 		mods = &mTargets;
@@ -218,8 +216,9 @@ void _stdcall KnockbackRemoveMod(TGameObj* object, DWORD on) {
 		return;
 	}
 	for (DWORD i = 0; i < mods->size(); i++) {
-		if ((*mods)[i].id == id) {
+		if ((*mods)[i].id == object->ID) {
 			mods->erase(mods->begin() + i);
+			if (on == 0) SetNewEngineID(object); // revert to engine range id
 			return;
 		}
 	}
@@ -231,7 +230,7 @@ void _stdcall SetHitChanceMax(TGameObj* critter, DWORD maximum, DWORD mod) {
 		BaseHitChance.mod = mod;
 		return;
 	}
-
+	if (critter->pid >> 24 != OBJ_TYPE_CRITTER) return;
 	long id = SetObjectUniqueID(critter);
 	for (DWORD i = 0; i < HitChanceMods.size(); i++) {
 		if (id == HitChanceMods[i].id) {
@@ -270,7 +269,7 @@ void _stdcall SetPickpocketMax(TGameObj* critter, DWORD maximum, DWORD mod) {
 }
 
 void _stdcall SetNoBurstMode(TGameObj* critter, DWORD on) {
-	if (critter == *ptr_obj_dude) return;
+	if (critter == *ptr_obj_dude || critter->pid >> 24 != OBJ_TYPE_CRITTER) return;
 
 	long id = SetObjectUniqueID(critter);
 	for (DWORD i = 0; i < NoBursts.size(); i++) {
@@ -349,7 +348,7 @@ void Knockback_OnGameLoad() {
 	BasePickpocket.mod = 0;
 	mTargets.clear();
 	mAttackers.clear();
-	mWeapons.clear();
+	Knockback_mWeapons.clear();
 	HitChanceMods.clear();
 	PickpocketMods.clear();
 	NoBursts.clear();
diff --git a/sfall/Knockback.h b/sfall/Knockback.h
index 7fb72c25..03e0cd22 100644
--- a/sfall/Knockback.h
+++ b/sfall/Knockback.h
@@ -18,6 +18,14 @@
 
 #pragma once
 
+struct KnockbackModifier {
+	long id;
+	DWORD type;
+	double value;
+};
+
+extern std::vector<KnockbackModifier> Knockback_mWeapons;
+
 void _stdcall SetPickpocketMax(TGameObj* critter, DWORD maximum, DWORD mod);
 void _stdcall SetHitChanceMax(TGameObj* critter, DWORD maximum, DWORD mod);
 void _stdcall KnockbackSetMod(TGameObj* object, DWORD type, float val, DWORD on);
diff --git a/sfall/ScriptExtender.cpp b/sfall/ScriptExtender.cpp
index 21cede4e..405ee01d 100644
--- a/sfall/ScriptExtender.cpp
+++ b/sfall/ScriptExtender.cpp
@@ -31,6 +31,7 @@
 #include "FalloutEngine.h"
 #include "HookScripts.h"
 #include "input.h"
+#include "Knockback.h"
 #include "LoadGameHook.h"
 #include "Logging.h"
 #include "ScriptExtender.h"
@@ -402,7 +403,7 @@ static const SfallOpcodeMetadata opcodeMetaArray[] = {
 	{sf_set_map_enter_position, "set_map_enter_position", {DATATYPE_MASK_INT, DATATYPE_MASK_INT, DATATYPE_MASK_INT}},
 	{sf_set_object_data,        "set_object_data",        {DATATYPE_MASK_VALID_OBJ, DATATYPE_MASK_INT, DATATYPE_MASK_INT}},
 	{sf_set_outline,            "set_outline",            {DATATYPE_MASK_VALID_OBJ, DATATYPE_MASK_INT}},
-	{sf_set_unique_id,          "set_unique_id",          {DATATYPE_MASK_VALID_OBJ}},
+	{sf_set_unique_id,          "set_unique_id",          {DATATYPE_MASK_VALID_OBJ, DATATYPE_MASK_INT}},
 	{sf_spatial_radius,         "spatial_radius",         {DATATYPE_MASK_VALID_OBJ}},
 	{sf_unjam_lock,             "unjam_lock",             {DATATYPE_MASK_VALID_OBJ}},
 	#ifndef NDEBUG
@@ -1269,6 +1270,45 @@ long SetObjectUniqueID(TGameObj* obj) {
 	return objUniqueID;
 }
 
+// Assigns a unique ID in the negative range (0x8FFFFFFF - 0xFFFFFFFE)
+long SetSpecialID(TGameObj* obj) {
+	long id = obj->ID;
+	if (id < -1 || id > UID_START) return id;
+
+	if ((DWORD)objUniqueID >= UID_END) objUniqueID = UID_START;
+	id = ++objUniqueID + UID_END;
+	obj->ID = id;
+	return id;
+}
+
+void SetNewEngineID(TGameObj* obj) {
+	if (obj->ID > UID_START) return;
+	obj->ID = NewObjId();
+}
+
+static bool __fastcall CheckSpecialID(long id) {
+	if (Knockback_mWeapons.empty()) return false;
+	for (std::vector<KnockbackModifier>::iterator it = Knockback_mWeapons.begin(); it != Knockback_mWeapons.end(); ++it) {
+		if (id == it->id) return true;
+	}
+	return false;
+}
+
+static void __declspec(naked) item_identical_hack() {
+	__asm {
+		mov  ecx, [edi]; // item id
+		cmp  ecx, UID_START; // start unique ID
+		jg   notIdentical;
+		call CheckSpecialID;
+		test al, al;
+		jnz  notIdentical;
+		mov  eax, [esi + 0x78]; // scriptID
+		cmp  eax, ebx;
+notIdentical:
+		retn; // if ZF == 0 then item is not identical
+	}
+}
+
 static void __declspec(naked) new_obj_id_hook() {
 	__asm {
 		mov  eax, 83535;
@@ -1316,6 +1356,10 @@ void ScriptExtenderSetup() {
 	HookCall(0x4A38A5, new_obj_id_hook);
 	SafeWrite8(0x4A38B3, 0x90); // fix ID increment
 
+	//if (GetPrivateProfileIntA("Misc", "StackableUniqueItems", 0, ini) == 0) {
+		MakeCall(0x477A0E, item_identical_hack); // don't put to item stack
+	//}
+
 	arraysBehavior = GetPrivateProfileIntA("Misc", "arraysBehavior", 1, ini);
 	if (arraysBehavior > 0) {
 		arraysBehavior = 1; // only 1 and 0 allowed at this time
diff --git a/sfall/ScriptExtender.h b/sfall/ScriptExtender.h
index 3beca0bb..a51fa0b7 100644
--- a/sfall/ScriptExtender.h
+++ b/sfall/ScriptExtender.h
@@ -98,6 +98,8 @@ extern DWORD AvailableGlobalScriptTypes;
 // object's unique id
 extern long objUniqueID;
 long SetObjectUniqueID(TGameObj* obj);
+long SetSpecialID(TGameObj* obj);
+void SetNewEngineID(TGameObj* obj);
 
 // types for script variables
 #define VAR_TYPE_INT    (0xC001)
diff --git a/sfall/ScriptOps/MetaruleOp.hpp b/sfall/ScriptOps/MetaruleOp.hpp
index 10c77725..329d5219 100644
--- a/sfall/ScriptOps/MetaruleOp.hpp
+++ b/sfall/ScriptOps/MetaruleOp.hpp
@@ -133,7 +133,7 @@ static const SfallMetarule metaruleArray[] = {
 	{"set_map_enter_position",  sf_set_map_enter_position,  3, 3},
 	{"set_object_data",         sf_set_object_data,         3, 3},
 	{"set_outline",             sf_set_outline,             2, 2},
-	{"set_unique_id",           sf_set_unique_id,           1, 1},
+	{"set_unique_id",           sf_set_unique_id,           1, 2},
 	{"spatial_radius",          sf_spatial_radius,          1, 1},
 	{"tile_refresh_display",    sf_tile_refresh_display,    0, 0},
 	{"unjam_lock",              sf_unjam_lock,              1, 1},
diff --git a/sfall/ScriptOps/ObjectsOps.hpp b/sfall/ScriptOps/ObjectsOps.hpp
index 74757db4..e05bc983 100644
--- a/sfall/ScriptOps/ObjectsOps.hpp
+++ b/sfall/ScriptOps/ObjectsOps.hpp
@@ -645,5 +645,13 @@ static void sf_set_object_data() {
 }
 
 static void sf_set_unique_id() {
-	opHandler.setReturn(SetObjectUniqueID(opHandler.arg(0).asObject()), DATATYPE_INT);
+	TGameObj* obj = opHandler.arg(0).asObject();
+	long id;
+	if (opHandler.numArgs() == 2 && opHandler.arg(1).asInt() == -1) {
+		id = NewObjId();
+		obj->ID = id;
+	} else {
+		id = SetObjectUniqueID(obj);
+	}
+	opHandler.setReturn(id, DATATYPE_INT);
 }