diff --git a/.swift-version b/.swift-version
index a3ec5a4..5186d07 100644
--- a/.swift-version
+++ b/.swift-version
@@ -1 +1 @@
-3.2
+4.0
diff --git a/Surge.xcodeproj/project.pbxproj b/Surge.xcodeproj/project.pbxproj
index b9c4605..de6418b 100644
--- a/Surge.xcodeproj/project.pbxproj
+++ b/Surge.xcodeproj/project.pbxproj
@@ -247,11 +247,11 @@
 				TargetAttributes = {
 					F84A6AAD19A9A72F007B53E1 = {
 						CreatedOnToolsVersion = 6.0;
-						LastSwiftMigration = 0800;
+						LastSwiftMigration = 0900;
 					};
 					F8A1E1A919917A79009735E2 = {
 						CreatedOnToolsVersion = 6.0;
-						LastSwiftMigration = 0800;
+						LastSwiftMigration = 0900;
 						ProvisioningStyle = Manual;
 					};
 				};
@@ -349,7 +349,6 @@
 				PRODUCT_BUNDLE_IDENTIFIER = "com.mattt.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-				SWIFT_VERSION = 3.0;
 			};
 			name = Debug;
 		};
@@ -361,7 +360,6 @@
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/Frameworks @loader_path/Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = "com.mattt.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
 			};
 			name = Release;
 		};
@@ -415,6 +413,8 @@
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = iphoneos;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
+				SWIFT_SWIFT3_OBJC_INFERENCE = Off;
+				SWIFT_VERSION = 4.0;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				VERSIONING_SYSTEM = "apple-generic";
 				VERSION_INFO_PREFIX = "";
@@ -463,6 +463,8 @@
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = iphoneos;
 				SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
+				SWIFT_SWIFT3_OBJC_INFERENCE = Off;
+				SWIFT_VERSION = 4.0;
 				TARGETED_DEVICE_FAMILY = "1,2";
 				VALIDATE_PRODUCT = YES;
 				VERSIONING_SYSTEM = "apple-generic";
@@ -485,7 +487,6 @@
 				PRODUCT_BUNDLE_IDENTIFIER = "com.mattt.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SKIP_INSTALL = YES;
-				SWIFT_VERSION = 3.0;
 			};
 			name = Debug;
 		};
@@ -504,7 +505,6 @@
 				PRODUCT_BUNDLE_IDENTIFIER = "com.mattt.$(PRODUCT_NAME:rfc1034identifier)";
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SKIP_INSTALL = YES;
-				SWIFT_VERSION = 3.0;
 			};
 			name = Release;
 		};
diff --git a/Tests/SurgeTests/XCTestCase+Surge.swift b/Tests/SurgeTests/XCTestCase+Surge.swift
index 464db9c..23a173e 100644
--- a/Tests/SurgeTests/XCTestCase+Surge.swift
+++ b/Tests/SurgeTests/XCTestCase+Surge.swift
@@ -25,7 +25,7 @@ extension XCTestCase {
     func measureAndValidateMappedFunctionWithAccuracy<C : Collection>(source: C, member: (C.Iterator.Element) -> (C.Iterator.Element), mapped: @escaping (C) -> ([C.Iterator.Element]), accuracy: C.Iterator.Element) where C.Iterator.Element: ExpressibleByFloatLiteral & FloatingPoint {
         var expected = source.map(member)
 
-        var actual: [C.Generator.Element] = []
+        var actual: [C.Iterator.Element] = []
         self.measure {
             actual = mapped(source)
         }