diff --git a/Package.swift b/Package.swift
index 75c6e47..b8ccca4 100644
--- a/Package.swift
+++ b/Package.swift
@@ -16,5 +16,5 @@ let package = Package(
         .target(name: "ReactiveTask", dependencies: ["Result", "ReactiveSwift"], path: "Sources"),
         .testTarget(name: "ReactiveTaskTests", dependencies: ["ReactiveTask", "Quick", "Nimble"]),
     ],
-    swiftLanguageVersions: [3]
+    swiftLanguageVersions: [4]
 )
diff --git a/ReactiveTask.xcodeproj/project.pbxproj b/ReactiveTask.xcodeproj/project.pbxproj
index 519eedb..c733f5c 100644
--- a/ReactiveTask.xcodeproj/project.pbxproj
+++ b/ReactiveTask.xcodeproj/project.pbxproj
@@ -370,7 +370,8 @@
 				MACOSX_DEPLOYMENT_TARGET = 10.9;
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = macosx;
-				SWIFT_VERSION = 2.3;
+				SWIFT_SWIFT3_OBJC_INFERENCE = Off;
+				SWIFT_VERSION = 4.0;
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
 			};
@@ -390,7 +391,8 @@
 				GCC_NO_COMMON_BLOCKS = YES;
 				MACOSX_DEPLOYMENT_TARGET = 10.9;
 				SDKROOT = macosx;
-				SWIFT_VERSION = 2.3;
+				SWIFT_SWIFT3_OBJC_INFERENCE = Off;
+				SWIFT_VERSION = 4.0;
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
 			};
@@ -406,7 +408,6 @@
 				INFOPLIST_FILE = Sources/Info.plist;
 				PRODUCT_BUNDLE_IDENTIFIER = "org.carthage.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
 			};
 			name = Debug;
 		};
@@ -420,7 +421,6 @@
 				INFOPLIST_FILE = Sources/Info.plist;
 				PRODUCT_BUNDLE_IDENTIFIER = "org.carthage.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
 			};
 			name = Release;
 		};
@@ -435,7 +435,6 @@
 				INFOPLIST_FILE = Tests/ReactiveTaskTests/Info.plist;
 				PRODUCT_BUNDLE_IDENTIFIER = "org.carthage.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
 			};
 			name = Debug;
 		};
@@ -450,7 +449,6 @@
 				INFOPLIST_FILE = Tests/ReactiveTaskTests/Info.plist;
 				PRODUCT_BUNDLE_IDENTIFIER = "org.carthage.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
 			};
 			name = Release;
 		};
@@ -468,7 +466,8 @@
 				GCC_NO_COMMON_BLOCKS = YES;
 				MACOSX_DEPLOYMENT_TARGET = 10.9;
 				SDKROOT = macosx;
-				SWIFT_VERSION = 2.3;
+				SWIFT_SWIFT3_OBJC_INFERENCE = Off;
+				SWIFT_VERSION = 4.0;
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
 			};
@@ -484,7 +483,6 @@
 				INFOPLIST_FILE = Sources/Info.plist;
 				PRODUCT_BUNDLE_IDENTIFIER = "org.carthage.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
 			};
 			name = Test;
 		};
@@ -499,7 +497,6 @@
 				INFOPLIST_FILE = Tests/ReactiveTaskTests/Info.plist;
 				PRODUCT_BUNDLE_IDENTIFIER = "org.carthage.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
 			};
 			name = Test;
 		};
@@ -517,7 +514,8 @@
 				GCC_NO_COMMON_BLOCKS = YES;
 				MACOSX_DEPLOYMENT_TARGET = 10.9;
 				SDKROOT = macosx;
-				SWIFT_VERSION = 2.3;
+				SWIFT_SWIFT3_OBJC_INFERENCE = Off;
+				SWIFT_VERSION = 4.0;
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
 			};
@@ -533,7 +531,6 @@
 				INFOPLIST_FILE = Sources/Info.plist;
 				PRODUCT_BUNDLE_IDENTIFIER = "org.carthage.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
 			};
 			name = Profile;
 		};
@@ -548,7 +545,6 @@
 				INFOPLIST_FILE = Tests/ReactiveTaskTests/Info.plist;
 				PRODUCT_BUNDLE_IDENTIFIER = "org.carthage.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
 			};
 			name = Profile;
 		};
diff --git a/Sources/Task.swift b/Sources/Task.swift
index e69efdf..10edd04 100644
--- a/Sources/Task.swift
+++ b/Sources/Task.swift
@@ -180,12 +180,10 @@ private final class Pipe {
 			channel.setLimit(lowWater: 1)
 			channel.read(offset: 0, length: Int.max, queue: self.queue) { (done, dispatchData, error) in
 				if let dispatchData = dispatchData {
-					let bytes = UnsafeMutablePointer<UInt8>.allocate(capacity: dispatchData.count)
-					dispatchData.copyBytes(to: bytes, count: dispatchData.count)
-					let data = Data(bytes: bytes, count: dispatchData.count)
-					bytes.deinitialize(count: dispatchData.count)
-					bytes.deallocate(capacity: dispatchData.count)
-					
+					// Cast DispatchData to Data.
+					// See https://gist.github.com/mayoff/6e35e263b9ddd04d9b77e5261212be19.
+					let data = dispatchData as Any as! NSData as Data
+
 					observer.send(value: data)
 				}
 
@@ -235,7 +233,7 @@ private final class Pipe {
 
 				signal.observe(Signal.Observer(value: { data in
 					let dispatchData = data.withUnsafeBytes { (bytes: UnsafePointer<UInt8>) -> DispatchData in
-						let buffer = UnsafeBufferPointer(start: bytes, count: data.count)
+						let buffer = UnsafeRawBufferPointer(start: bytes, count: data.count)
 						return DispatchData(bytes: buffer)
 					}