diff --git a/SwiftTask.xcodeproj/project.pbxproj b/SwiftTask.xcodeproj/project.pbxproj
index 35ec5a4..ac6b1ab 100644
--- a/SwiftTask.xcodeproj/project.pbxproj
+++ b/SwiftTask.xcodeproj/project.pbxproj
@@ -303,7 +303,7 @@
 			isa = PBXProject;
 			attributes = {
 				LastSwiftUpdateCheck = 0700;
-				LastUpgradeCheck = 0800;
+				LastUpgradeCheck = 0900;
 				ORGANIZATIONNAME = "Yasuhiro Inami";
 				TargetAttributes = {
 					1F46DED3199EDF1000F97868 = {
@@ -433,13 +433,21 @@
 				CLANG_CXX_LIBRARY = "libc++";
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_ENABLE_OBJC_ARC = YES;
+				CLANG_WARN_BLOCK_CAPTURE_AUTORELEASING = YES;
 				CLANG_WARN_BOOL_CONVERSION = YES;
+				CLANG_WARN_COMMA = YES;
 				CLANG_WARN_CONSTANT_CONVERSION = YES;
 				CLANG_WARN_DIRECT_OBJC_ISA_USAGE = YES_ERROR;
 				CLANG_WARN_EMPTY_BODY = YES;
 				CLANG_WARN_ENUM_CONVERSION = YES;
+				CLANG_WARN_INFINITE_RECURSION = YES;
 				CLANG_WARN_INT_CONVERSION = YES;
+				CLANG_WARN_NON_LITERAL_NULL_CONVERSION = YES;
+				CLANG_WARN_OBJC_LITERAL_CONVERSION = YES;
 				CLANG_WARN_OBJC_ROOT_CLASS = YES_ERROR;
+				CLANG_WARN_RANGE_LOOP_ANALYSIS = YES;
+				CLANG_WARN_STRICT_PROTOTYPES = YES;
+				CLANG_WARN_SUSPICIOUS_MOVE = YES;
 				CLANG_WARN_UNREACHABLE_CODE = YES;
 				CLANG_WARN__DUPLICATE_METHOD_MATCH = YES;
 				COPY_PHASE_STRIP = NO;
@@ -478,13 +486,21 @@
 				CLANG_CXX_LIBRARY = "libc++";
 				CLANG_ENABLE_MODULES = YES;
 				CLANG_ENABLE_OBJC_ARC = YES;
+				CLANG_WARN_BLOCK_CAPTURE_AUTORELEASING = YES;
 				CLANG_WARN_BOOL_CONVERSION = YES;
+				CLANG_WARN_COMMA = YES;
 				CLANG_WARN_CONSTANT_CONVERSION = YES;
 				CLANG_WARN_DIRECT_OBJC_ISA_USAGE = YES_ERROR;
 				CLANG_WARN_EMPTY_BODY = YES;
 				CLANG_WARN_ENUM_CONVERSION = YES;
+				CLANG_WARN_INFINITE_RECURSION = YES;
 				CLANG_WARN_INT_CONVERSION = YES;
+				CLANG_WARN_NON_LITERAL_NULL_CONVERSION = YES;
+				CLANG_WARN_OBJC_LITERAL_CONVERSION = YES;
 				CLANG_WARN_OBJC_ROOT_CLASS = YES_ERROR;
+				CLANG_WARN_RANGE_LOOP_ANALYSIS = YES;
+				CLANG_WARN_STRICT_PROTOTYPES = YES;
+				CLANG_WARN_SUSPICIOUS_MOVE = YES;
 				CLANG_WARN_UNREACHABLE_CODE = YES;
 				CLANG_WARN__DUPLICATE_METHOD_MATCH = YES;
 				COPY_PHASE_STRIP = YES;
@@ -522,6 +538,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = "com.inamiy.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(PROJECT_NAME)";
 				SKIP_INSTALL = YES;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -541,6 +558,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = "com.inamiy.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(PROJECT_NAME)";
 				SKIP_INSTALL = YES;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
 		};
@@ -554,9 +572,11 @@
 					"$(inherited)",
 				);
 				INFOPLIST_FILE = SwiftTaskTests/Info.plist;
+				MACOSX_DEPLOYMENT_TARGET = 10.10;
 				PRODUCT_BUNDLE_IDENTIFIER = "com.inamiy.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = macosx;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -566,9 +586,11 @@
 			buildSettings = {
 				COMBINE_HIDPI_IMAGES = YES;
 				INFOPLIST_FILE = SwiftTaskTests/Info.plist;
+				MACOSX_DEPLOYMENT_TARGET = 10.10;
 				PRODUCT_BUNDLE_IDENTIFIER = "com.inamiy.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = macosx;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
 		};
@@ -581,9 +603,11 @@
 					"$(inherited)",
 				);
 				INFOPLIST_FILE = SwiftTaskTests/Info.plist;
+				MACOSX_DEPLOYMENT_TARGET = 10.10;
 				PRODUCT_BUNDLE_IDENTIFIER = "com.inamiy.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = iphoneos;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -592,9 +616,11 @@
 			baseConfigurationReference = 1FFADCDE1C5CEC1B000B66BE /* UniversalFramework_Test.xcconfig */;
 			buildSettings = {
 				INFOPLIST_FILE = SwiftTaskTests/Info.plist;
+				MACOSX_DEPLOYMENT_TARGET = 10.10;
 				PRODUCT_BUNDLE_IDENTIFIER = "com.inamiy.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SDKROOT = iphoneos;
+				SWIFT_VERSION = 4.0;
 				VALIDATE_PRODUCT = YES;
 			};
 			name = Release;
diff --git a/SwiftTask.xcodeproj/xcshareddata/xcschemes/SwiftTask.xcscheme b/SwiftTask.xcodeproj/xcshareddata/xcschemes/SwiftTask.xcscheme
index 09eb84c..234c8fd 100644
--- a/SwiftTask.xcodeproj/xcshareddata/xcschemes/SwiftTask.xcscheme
+++ b/SwiftTask.xcodeproj/xcshareddata/xcschemes/SwiftTask.xcscheme
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <Scheme
-   LastUpgradeVersion = "0800"
+   LastUpgradeVersion = "0900"
    version = "1.3">
    <BuildAction
       parallelizeBuildables = "YES"
@@ -26,6 +26,7 @@
       buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      language = ""
       shouldUseLaunchSchemeArgsEnv = "YES">
       <Testables>
          <TestableReference
@@ -55,6 +56,7 @@
       buildConfiguration = "Debug"
       selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
       selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      language = ""
       launchStyle = "0"
       useCustomWorkingDirectory = "NO"
       ignoresPersistentStateOnLaunch = "NO"
diff --git a/SwiftTask/SwiftTask.swift b/SwiftTask/SwiftTask.swift
index e57e50a..deccb8b 100644
--- a/SwiftTask/SwiftTask.swift
+++ b/SwiftTask/SwiftTask.swift
@@ -380,9 +380,10 @@ open class Task<Progress, Value, Error>: Cancellable, CustomStringConvertible
     {
         var token: _HandlerToken? = nil
         self._machine.addProgressTupleHandler(&token, progressClosure)
+        weak var machine = _machine
         
-        canceller = C { [weak self] in
-            self?._machine.removeProgressTupleHandler(token)
+        canceller = C {
+            machine?.removeProgressTupleHandler(token)
         }
         
         return self
diff --git a/SwiftTask/_StateMachine.swift b/SwiftTask/_StateMachine.swift
index 1a19b1e..b7cc569 100644
--- a/SwiftTask/_StateMachine.swift
+++ b/SwiftTask/_StateMachine.swift
@@ -114,7 +114,7 @@ internal class _StateMachine<Progress, Value, Error>
             }
             
             for handler in self._progressTupleHandlers {
-                handler(oldProgress: oldProgress, newProgress: progress)
+                handler((oldProgress: oldProgress, newProgress: progress))
             }
         }
     }
diff --git a/SwiftTaskTests/SwiftTaskTests.swift b/SwiftTaskTests/SwiftTaskTests.swift
index 50b689e..60d9342 100644
--- a/SwiftTaskTests/SwiftTaskTests.swift
+++ b/SwiftTaskTests/SwiftTaskTests.swift
@@ -536,7 +536,7 @@ class SwiftTaskTests: _TestCase
         let task = _interruptableTask(progressCount: 5)    // 1st async task (5 progresses)
         
         // chain async-task with then
-        let task3 = task.then { _ -> _InterruptableTask in
+        let task3 = task.then { _,_ -> _InterruptableTask in
             let task2 = _interruptableTask(progressCount: 7)    // 2st async task (7 progresses)
             return task2
         }
@@ -760,7 +760,7 @@ class SwiftTaskTests: _TestCase
         weak var innerTask: _InterruptableTask?
         
         // chain async-task with `then`
-        let task2 = task.then { _ -> _InterruptableTask in
+        let task2 = task.then { _,_ -> _InterruptableTask in
             innerTask = _interruptableTask(progressCount: 5)
             return innerTask!
         }