diff --git a/src/Catty/DataModel/Bricks/Look/SetBackgroundByIndexBrick.swift b/src/Catty/DataModel/Bricks/Look/SetBackgroundByIndexBrick.swift
index dd0e89f046..5ef4e99741 100644
--- a/src/Catty/DataModel/Bricks/Look/SetBackgroundByIndexBrick.swift
+++ b/src/Catty/DataModel/Bricks/Look/SetBackgroundByIndexBrick.swift
@@ -24,9 +24,10 @@
 
 @objcMembers class SetBackgroundByIndexBrick: Brick, BrickProtocol, BrickFormulaProtocol {
 
-    var backgroundIndex: Formula?
+    var backgroundIndex: Formula
 
     override required init() {
+        self.backgroundIndex = Formula(integer: 1)
         super.init()
     }
 
@@ -39,7 +40,7 @@
     }
 
     override func getRequiredResources() -> Int {
-        backgroundIndex?.getRequiredResources() ?? ResourceType.noResources.rawValue
+        backgroundIndex.getRequiredResources()
     }
 
     override func brickCell() -> BrickCellProtocol.Type! {
@@ -55,7 +56,7 @@
     }
 
     func getFormulas() -> [Formula]! {
-        [backgroundIndex!]
+        [backgroundIndex]
     }
 
     override func setDefaultValuesFor(_ spriteObject: SpriteObject!) {
diff --git a/src/Catty/DataModel/Bricks/Look/SetLookByIndexBrick.swift b/src/Catty/DataModel/Bricks/Look/SetLookByIndexBrick.swift
index 3969604848..3351f9eab5 100644
--- a/src/Catty/DataModel/Bricks/Look/SetLookByIndexBrick.swift
+++ b/src/Catty/DataModel/Bricks/Look/SetLookByIndexBrick.swift
@@ -24,9 +24,10 @@
 
 @objcMembers class SetLookByIndexBrick: Brick, BrickProtocol, BrickFormulaProtocol {
 
-    var lookIndex: Formula?
+    var lookIndex: Formula
 
     override required init() {
+        self.lookIndex = Formula(integer: kBackgroundObjects)
         super.init()
     }
 
@@ -55,7 +56,7 @@
     }
 
     func getFormulas() -> [Formula]! {
-        [lookIndex!]
+        [lookIndex]
     }
 
     override func setDefaultValuesFor(_ spriteObject: SpriteObject!) {
diff --git a/src/Catty/PlayerEngine/Instructions/Look/SetBackgroundByIndexBrick+Instruction.swift b/src/Catty/PlayerEngine/Instructions/Look/SetBackgroundByIndexBrick+Instruction.swift
index 67d5a8df53..dbbe60f9be 100644
--- a/src/Catty/PlayerEngine/Instructions/Look/SetBackgroundByIndexBrick+Instruction.swift
+++ b/src/Catty/PlayerEngine/Instructions/Look/SetBackgroundByIndexBrick+Instruction.swift
@@ -33,8 +33,7 @@
             let spriteNode = object.spriteNode
             else { fatalError("This should never happen!") }
         return {
-            guard let backgroundIndex = self.backgroundIndex else { return }
-            let index = formulaInterpreter.interpretInteger(backgroundIndex, for: object)
+            let index = formulaInterpreter.interpretInteger(self.backgroundIndex, for: object)
             guard let look = spriteNode.look(for: index) else { return }
             var image = imageCache.cachedImage(forPath: self.path(for: look))
 
diff --git a/src/Catty/PlayerEngine/Instructions/Look/SetLookByIndexBrick+Instruction.swift b/src/Catty/PlayerEngine/Instructions/Look/SetLookByIndexBrick+Instruction.swift
index 2230ca51e0..97385ebf3e 100644
--- a/src/Catty/PlayerEngine/Instructions/Look/SetLookByIndexBrick+Instruction.swift
+++ b/src/Catty/PlayerEngine/Instructions/Look/SetLookByIndexBrick+Instruction.swift
@@ -28,12 +28,11 @@ extension SetLookByIndexBrick: CBInstructionProtocol {
 
     func actionBlock(_ formulaInterpreter: FormulaInterpreterProtocol) -> () -> Void {
         guard let object = self.script?.object,
-            let spriteNode = object.spriteNode,
-            let formula = self.lookIndex
+            let spriteNode = object.spriteNode
             else { fatalError("This should never happen!") }
 
         return {
-            let lookIndex = formulaInterpreter.interpretInteger(formula, for: object)
+            let lookIndex = formulaInterpreter.interpretInteger(self.lookIndex, for: object)
             guard let lookAtIndex = spriteNode.look(for: lookIndex) else { return }
 
             let cache = RuntimeImageCache.shared()
diff --git a/src/Catty/XML/XMLHandler/Bricks/LookBricks/SetBackgroundByIndexBrick+CBXMLHandler.swift b/src/Catty/XML/XMLHandler/Bricks/LookBricks/SetBackgroundByIndexBrick+CBXMLHandler.swift
index 33d9581ab6..9885cd0f14 100644
--- a/src/Catty/XML/XMLHandler/Bricks/LookBricks/SetBackgroundByIndexBrick+CBXMLHandler.swift
+++ b/src/Catty/XML/XMLHandler/Bricks/LookBricks/SetBackgroundByIndexBrick+CBXMLHandler.swift
@@ -42,7 +42,7 @@ extension SetBackgroundByIndexBrick: CBXMLNodeProtocol {
     func xmlElement(with context: CBXMLSerializerContext) -> GDataXMLElement? {
         let brick = super.xmlElement(for: "SetBackgroundByIndexBrick", with: context)
         let formulaList = GDataXMLElement(name: "formulaList", context: context)
-        let formula = self.backgroundIndex?.xmlElement(with: context)
+        let formula = self.backgroundIndex.xmlElement(with: context)
         formula?.addAttribute(GDataXMLElement(name: "category", stringValue: "BACKGROUND_INDEX", context: nil))
         formulaList?.addChild(formula, context: context)
         brick?.addChild(formulaList, context: context)
diff --git a/src/Catty/XML/XMLHandler/Bricks/LookBricks/SetLookByIndexBrick+CBXMLHandler.swift b/src/Catty/XML/XMLHandler/Bricks/LookBricks/SetLookByIndexBrick+CBXMLHandler.swift
index acf50344a8..544af6dd66 100644
--- a/src/Catty/XML/XMLHandler/Bricks/LookBricks/SetLookByIndexBrick+CBXMLHandler.swift
+++ b/src/Catty/XML/XMLHandler/Bricks/LookBricks/SetLookByIndexBrick+CBXMLHandler.swift
@@ -26,14 +26,14 @@ extension SetLookByIndexBrick: CBXMLNodeProtocol {
         CBXMLParserHelper.validate(xmlElement, forNumberOfChildNodes: 1, andFormulaListWithTotalNumberOfFormulas: 1)
         let formula = CBXMLParserHelper.formula(in: xmlElement, forCategoryName: "LOOK_INDEX", with: context)
         let brick = self.init()
-        brick.lookIndex = formula
+        brick.setFormula(formula, forLineNumber: 0, andParameterNumber: 0)
         return brick
     }
 
     func xmlElement(with context: CBXMLSerializerContext) -> GDataXMLElement? {
         let brick = super.xmlElement(for: "SetLookByIndexBrick", with: context)
         let formulaList = GDataXMLElement(name: "formulaList", context: context)
-        let formula = self.lookIndex?.xmlElement(with: context)
+        let formula = self.lookIndex.xmlElement(with: context)
         formula?.addAttribute(GDataXMLElement(name: "category", stringValue: "LOOK_INDEX", context: nil))
         formulaList?.addChild(formula, context: context)
         brick?.addChild(formulaList, context: context)