diff --git a/.travis.yml b/.travis.yml
index 455a37f..063ff8f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,4 +1,4 @@
 language: objective-c
-osx_image: xcode9
+osx_image: xcode9.3
 script:
 - swift build
diff --git a/Benchmarking/Shuffle.swift b/Benchmarking/Shuffle.swift
index 34a348c..dc32a2a 100644
--- a/Benchmarking/Shuffle.swift
+++ b/Benchmarking/Shuffle.swift
@@ -28,19 +28,19 @@ extension FixedWidthInteger {
     }
 }
 
-extension RandomAccessCollection where IndexDistance: FixedWidthInteger {
+extension RandomAccessCollection {
     public func randomElement() -> Element {
         precondition(count > 0)
-        let offset = Self.IndexDistance.random(below: count)
+        let offset = Int.random(below: count)
         let index = self.index(self.startIndex, offsetBy: offset)
         return self[index]
     }
 }
 
-extension RandomAccessCollection where Self: MutableCollection, IndexDistance: FixedWidthInteger {
+extension RandomAccessCollection where Self: MutableCollection {
     public mutating func shuffle() {
         for i in indices {
-            let offset = IndexDistance.random(below: self.distance(from: i, to: self.endIndex))
+            let offset = Int.random(below: self.distance(from: i, to: self.endIndex))
             let j = self.index(i, offsetBy: offset)
             if i != j {
                 self.swapAt(i, j)