diff --git a/Example/Tests/DeviceLayoutConstraintTests.swift b/Example/Tests/DeviceLayoutConstraintTests.swift
index b234eb0..80e1eb4 100644
--- a/Example/Tests/DeviceLayoutConstraintTests.swift
+++ b/Example/Tests/DeviceLayoutConstraintTests.swift
@@ -8,6 +8,7 @@
 
 import XCTest
 
+import Device
 import Quick
 import Nimble
 
@@ -39,7 +40,7 @@ class DeviceLayoutConstraintTests: QuickSpec {
         describe("DeviceLayoutConstraint") {
             context("when use iPhone6") {
                 beforeEach {
-                    sut.deviceSize = .screen5_5Inch
+                    sut.expectedDeviceSize = .screen5_5Inch
                     sut.inch5_5 = Expected.Constant.inch5_5
                 }
                 
@@ -60,7 +61,7 @@ class DeviceLayoutConstraintTests: QuickSpec {
             
             context("when deviceSize is 4inch device") {
                 beforeEach {
-                    sut.deviceSize = .screen4Inch
+                    sut.expectedDeviceSize = .screen4Inch
                 }
                 
                 context("when set constant per deviceSize") {
@@ -84,8 +85,14 @@ class DeviceLayoutConstraintTests: QuickSpec {
 }
 
 class DeviceLayoutConstraintSpy: DeviceLayoutConstraint {
+    var expectedDeviceSize: Size!
     var layoutIfNeededCalledCount: Int = 0
+    
     override open func layoutIfNeeded() {
         layoutIfNeededCalledCount += 1
     }
+    
+    override open func deviceSize() -> Size {
+        return expectedDeviceSize
+    }
 }
diff --git a/Sources/DeviceLayoutConstraint.swift b/Sources/DeviceLayoutConstraint.swift
index b84f0ea..02f2ec8 100644
--- a/Sources/DeviceLayoutConstraint.swift
+++ b/Sources/DeviceLayoutConstraint.swift
@@ -12,8 +12,6 @@ import Device
 
 class DeviceLayoutConstraint: NSLayoutConstraint {
     
-    open var deviceSize: Size = Device.size()
-    
     @IBInspectable var inch3_5: CGFloat = 0.0 { didSet { updateConstant(size: .screen3_5Inch, constant: inch3_5)}}
     @IBInspectable var inch4: CGFloat = 0.0 { didSet { updateConstant(size: .screen4Inch, constant: inch4)}}
     @IBInspectable var inch4_7: CGFloat = 0.0 { didSet { updateConstant(size: .screen4_7Inch, constant: inch4_7)}}
@@ -23,12 +21,16 @@ class DeviceLayoutConstraint: NSLayoutConstraint {
     @IBInspectable var inch12_9: CGFloat = 0.0 { didSet { updateConstant(size: .screen12_9Inch, constant: inch12_9)}}
     
     fileprivate func updateConstant(size: Size, constant: CGFloat) {
-        if size == self.deviceSize {
+        if size == deviceSize() {
             self.constant = constant
             layoutIfNeeded()
         }
     }
     
+    open func deviceSize() -> Size {
+        return Device.size()
+    }
+    
     open func layoutIfNeeded() {
         self.firstItem.layoutIfNeeded()
         self.secondItem?.layoutIfNeeded()