diff --git a/FoldingCell/FoldingCell/FoldingCell.swift b/FoldingCell/FoldingCell/FoldingCell.swift
index 7da21f5..8e291ed 100644
--- a/FoldingCell/FoldingCell/FoldingCell.swift
+++ b/FoldingCell/FoldingCell/FoldingCell.swift
@@ -365,7 +365,7 @@ open class FoldingCell: UITableViewCell {
         configureAnimationItems(.close)
         
         if durations.count < animationItemViews.count {
-            fatalError("wrong override func animationDuration(itemIndex:NSInteger, type:AnimationType)-> NSTimeInterval")
+            fatalError("wrong override func animationDuration(_ itemIndex: NSInteger, type :AnimationType) -> TimeInterval")
         }
         for index in 0 ..< animationItemViews.count {
             let animatedView = animationItemViews.reversed()[index]
diff --git a/README.md b/README.md
index 0110d84..e35b627 100644
--- a/README.md
+++ b/README.md
@@ -155,7 +155,7 @@ fileprivate struct C {
 
 6) Add this code to your new cell class
 ``` swift
-    override func animationDuration(itemIndex:NSInteger, type:AnimationType)-> NSTimeInterval {
+    override func animationDuration(_ itemIndex: NSInteger, type: AnimationType) -> TimeInterval {
 
         // durations count equal it itemCount
         let durations = [0.33, 0.26, 0.26] // timing animation for each view
diff --git a/docs/index.html b/docs/index.html
index 6d69988..0c15c5d 100644
--- a/docs/index.html
+++ b/docs/index.html
@@ -176,7 +176,7 @@
 
 <p>6) Add this code to your new cell class
 &rdquo;` swift
-    override func animationDuration(itemIndex:NSInteger, type:AnimationType)-&gt; NSTimeInterval {</p>
+    override func animationDuration(_ itemIndex: NSInteger, type: AnimationType)-&gt; TimeInterval {</p>
 <pre class="highlight plaintext"><code>    // durations count equal it itemCount
     let durations = [0.33, 0.26, 0.26] // timing animation for each view
     return durations[itemIndex]
diff --git a/docs/undocumented.txt b/docs/undocumented.txt
index 375d038..ab9e67d 100644
--- a/docs/undocumented.txt
+++ b/docs/undocumented.txt
@@ -7,6 +7,6 @@ FoldingCell.swift
 	required public init?(coder aDecoder: NSCoder)
 	override public func awakeFromNib()
 	public func isAnimating()->Bool
-	public func animationDuration(itemIndex:NSInteger, type:AnimationType)-> NSTimeInterval
+	public func animationDuration(_ itemIndex: NSInteger, type: AnimationType) -> TimeInterval
 	public class RotatedView: UIView
 	public class RotatedView : UIView