diff --git a/Source/Constraint.swift b/Source/Constraint.swift
index 90b532e..45f6014 100644
--- a/Source/Constraint.swift
+++ b/Source/Constraint.swift
@@ -201,7 +201,7 @@ public class Constraint {
         #endif
         
         // set install info
-        self.installInfo = ConstraintInstallInfo(view: installOnView, layoutConstraints: HashTable.weakObjects())
+        self.installInfo = ConstraintInstallInfo(view: installOnView, layoutConstraints: NSHashTable.weakObjects())
         
         // store which layout constraints are installed for this constraint
         for layoutConstraint in newLayoutConstraints {
@@ -219,8 +219,8 @@ public class Constraint {
             self.installInfo = nil
         }
         
-        guard let installedLayoutConstraints = self.installInfo?.layoutConstraints.allObjects as? [LayoutConstraint]
-              where installedLayoutConstraints.count > 0 else {
+        guard let installedLayoutConstraints = self.installInfo?.layoutConstraints.allObjects as? [LayoutConstraint],
+              installedLayoutConstraints.count > 0 else {
             return
         }
         
@@ -250,9 +250,9 @@ public class Constraint {
             }
         #endif
         
-        guard let layoutConstraints = self.installInfo?.layoutConstraints.allObjects as? [LayoutConstraint]
-            where layoutConstraints.count > 0 else {
-            return
+        guard let layoutConstraints = self.installInfo?.layoutConstraints.allObjects as? [LayoutConstraint],
+              layoutConstraints.count > 0 else {
+                return
         }
         
         NSLayoutConstraint.activate(layoutConstraints)
@@ -265,9 +265,9 @@ public class Constraint {
             }
         #endif
         
-        guard let layoutConstraints = self.installInfo?.layoutConstraints.allObjects as? [LayoutConstraint]
-            where layoutConstraints.count > 0 else {
-                return
+        guard let layoutConstraints = self.installInfo?.layoutConstraints.allObjects as? [LayoutConstraint],
+              layoutConstraints.count > 0 else {
+            return
         }
         
         NSLayoutConstraint.deactivate(layoutConstraints)
@@ -278,9 +278,9 @@ public class Constraint {
 private final class ConstraintInstallInfo {
     
     private weak var view: ConstraintView? = nil
-    private let layoutConstraints: HashTable<AnyObject>
+    private let layoutConstraints: NSHashTable<AnyObject>
     
-    private init(view: ConstraintView?, layoutConstraints: HashTable<AnyObject>) {
+    private init(view: ConstraintView?, layoutConstraints: NSHashTable<AnyObject>) {
         self.view = view
         self.layoutConstraints = layoutConstraints
     }
diff --git a/Source/ConstraintAttributes.swift b/Source/ConstraintAttributes.swift
index 89d7eab..3c4cf68 100644
--- a/Source/ConstraintAttributes.swift
+++ b/Source/ConstraintAttributes.swift
@@ -28,7 +28,7 @@
 #endif
 
 
-internal struct ConstraintAttributes: OptionSet, Boolean {
+internal struct ConstraintAttributes: OptionSet {
     
     internal init(rawValue: UInt) {
         self.rawValue = rawValue
diff --git a/Source/ConstraintItem.swift b/Source/ConstraintItem.swift
index 6ff291e..83733b5 100644
--- a/Source/ConstraintItem.swift
+++ b/Source/ConstraintItem.swift
@@ -56,8 +56,8 @@ public func ==(lhs: ConstraintItem, rhs: ConstraintItem) -> Bool {
     
     // must both have valid targets and identical attributes
     guard let target1 = lhs.target,
-          let target2 = rhs.target
-          where target1 === target2 && lhs.attributes == rhs.attributes else {
+          let target2 = rhs.target,
+          target1 === target2 && lhs.attributes == rhs.attributes else {
             return false
     }
     
diff --git a/Source/Debugging.swift b/Source/Debugging.swift
index e4bec9f..ff3a8a2 100644
--- a/Source/Debugging.swift
+++ b/Source/Debugging.swift
@@ -62,7 +62,7 @@ public extension LayoutConstraint {
             if self.constant > 0.0 {
                 description += " + \(self.constant)"
             } else if self.constant < 0.0 {
-                description += " - \(CGFloat.abs(self.constant))"
+                description += " - \(abs(self.constant))"
             }
         }