diff --git a/.swift-version b/.swift-version
index 1fc762a..d54e0b2 100644
--- a/.swift-version
+++ b/.swift-version
@@ -1 +1 @@
-3.0-PREVIEW-2
+3.0-PREVIEW-4
diff --git a/Result/Result.swift b/Result/Result.swift
index 5ab9c48..842fc94 100644
--- a/Result/Result.swift
+++ b/Result/Result.swift
@@ -1,7 +1,7 @@
 //  Copyright (c) 2015 Rob Rix. All rights reserved.
 
 /// An enum representing either a failure with an explanatory error, or a success with a result value.
-public enum Result<T, Error: ErrorProtocol>: ResultProtocol, CustomStringConvertible, CustomDebugStringConvertible {
+public enum Result<T, Error: Swift.Error>: ResultProtocol, CustomStringConvertible, CustomDebugStringConvertible {
 	case success(T)
 	case failure(Error)
 
@@ -157,8 +157,8 @@ public func `try`(_ function: String = #function, file: String = #file, line: In
 // MARK: - ErrorProtocolConvertible conformance
 	
 extension NSError: ErrorProtocolConvertible {
-	public static func error(from error: ErrorProtocol) -> Self {
-		func cast<T: NSError>(_ error: ErrorProtocol) -> T {
+	public static func error(from error: Swift.Error) -> Self {
+		func cast<T: NSError>(_ error: Swift.Error) -> T {
 			return error as! T
 		}
 
@@ -173,7 +173,7 @@ extension NSError: ErrorProtocolConvertible {
 /// This can be used to describe `Result`s where failures will never
 /// be generated. For example, `Result<Int, NoError>` describes a result that
 /// contains an `Int`eger and is guaranteed never to be a `Failure`.
-public enum NoError: ErrorProtocol { }
+public enum NoError: Swift.Error { }
 
 // MARK: - migration support
 extension Result {
@@ -190,7 +190,7 @@ extension Result {
 
 extension NSError {
 	@available(*, unavailable, renamed: "error(from:)")
-	public static func errorFromErrorType(_ error: ErrorProtocol) -> Self {
+	public static func errorFromErrorType(_ error: Swift.Error) -> Self {
 		fatalError()
 	}
 }
diff --git a/Result/ResultProtocol.swift b/Result/ResultProtocol.swift
index f4b0d28..ae33ffd 100644
--- a/Result/ResultProtocol.swift
+++ b/Result/ResultProtocol.swift
@@ -3,7 +3,7 @@
 /// A type that can represent either failure with an error or success with a result value.
 public protocol ResultProtocol {
 	associatedtype Value
-	associatedtype Error: ErrorProtocol
+	associatedtype Error: Swift.Error
 	
 	/// Constructs a successful result wrapping a `value`.
 	init(value: Value)
@@ -82,8 +82,8 @@ public extension ResultProtocol {
 }
 
 /// Protocol used to constrain `tryMap` to `Result`s with compatible `Error`s.
-public protocol ErrorProtocolConvertible: ErrorProtocol {
-	static func error(from error: ErrorProtocol) -> Self
+public protocol ErrorProtocolConvertible: Swift.Error {
+	static func error(from error: Swift.Error) -> Self
 }
 
 public extension ResultProtocol where Error: ErrorProtocolConvertible {
@@ -135,9 +135,9 @@ public func >>- <T: ResultProtocol, U> (result: T, transform: @noescape (T.Value
 
 /// Returns `true` if `left` and `right` are both `Success`es and their values are equal, or if `left` and `right` are both `Failure`s and their errors are equal.
 public func == <T: ResultProtocol where T.Value: Equatable, T.Error: Equatable> (left: T, right: T) -> Bool {
-	if let left = left.value, right = right.value {
+	if let left = left.value, let right = right.value {
 		return left == right
-	} else if let left = left.error, right = right.error {
+	} else if let left = left.error, let right = right.error {
 		return left == right
 	}
 	return false
@@ -163,7 +163,7 @@ public func ?? <T: ResultProtocol> (left: T, right: @autoclosure () -> T) -> T {
 public typealias ResultType = ResultProtocol
 
 @available(*, unavailable, renamed: "ErrorProtocol")
-public typealias ResultErrorType = ErrorProtocol
+public typealias ResultErrorType = Swift.Error
 
 @available(*, unavailable, renamed: "ErrorProtocolConvertible")
 public typealias ErrorTypeConvertible = ErrorProtocolConvertible
@@ -177,7 +177,7 @@ extension ResultProtocol {
 
 extension ErrorProtocolConvertible {
 	@available(*, unavailable, renamed: "error(from:)")
-	public static func errorFromErrorType(_ error: ErrorProtocol) -> Self {
+	public static func errorFromErrorType(_ error: Swift.Error) -> Self {
 		fatalError()
 	}
 }
diff --git a/Tests/Result/ResultTests.swift b/Tests/Result/ResultTests.swift
index 2989f9d..071f980 100644
--- a/Tests/Result/ResultTests.swift
+++ b/Tests/Result/ResultTests.swift
@@ -100,7 +100,7 @@ final class ResultTests: XCTestCase {
 	}
 
 	func testRecoverProducesRightForLeftFailure() {
-		struct Error: ErrorProtocol {}
+		struct Error: Swift.Error {}
 
 		let left = Result<String, Error>.failure(Error())
 		XCTAssertEqual(left.recover("right"), "right")
@@ -116,7 +116,7 @@ final class ResultTests: XCTestCase {
 	}
 
 	func testRecoverWithProducesRightSuccessForLeftFailureAndRightSuccess() {
-		struct Error: ErrorProtocol {}
+		struct Error: Swift.Error {}
 
 		let left = Result<String, Error>.failure(Error())
 		let right = Result<String, Error>.success("right")
@@ -125,7 +125,7 @@ final class ResultTests: XCTestCase {
 	}
 
 	func testRecoverWithProducesRightFailureForLeftFailureAndRightFailure() {
-		enum Error: ErrorProtocol { case left, right }
+		enum Error: Swift.Error { case left, right }
 
 		let left = Result<String, Error>.failure(.left)
 		let right = Result<String, Error>.failure(.right)
@@ -220,7 +220,7 @@ func attempt<T>(_ value: T, succeed: Bool, error: NSErrorPointer) -> T? {
 #endif
 
 func tryIsSuccess(_ text: String?) throws -> String {
-	guard let text = text where text == "success" else {
+	guard let text = text, text == "success" else {
 		throw error
 	}