diff --git a/Priority Queue/Tests/PriorityQueueTests.swift b/Priority Queue/Tests/PriorityQueueTests.swift
index 56536310d..e31fa3d07 100755
--- a/Priority Queue/Tests/PriorityQueueTests.swift	
+++ b/Priority Queue/Tests/PriorityQueueTests.swift	
@@ -11,6 +11,13 @@ private func < (m1: Message, m2: Message) -> Bool {
 }
 
 class PriorityQueueTest: XCTestCase {
+  func testSwift4() {
+    // last checked with Xcode 9.0b4
+    #if swift(>=4.0)
+      print("Hello, Swift 4!")
+    #endif
+  }
+  
   func testEmpty() {
     var queue = PriorityQueue<Message>(sort: <)
     XCTAssertTrue(queue.isEmpty)
diff --git a/Priority Queue/Tests/Tests.xcodeproj/project.pbxproj b/Priority Queue/Tests/Tests.xcodeproj/project.pbxproj
index 0f7d84be9..5ddfd574d 100644
--- a/Priority Queue/Tests/Tests.xcodeproj/project.pbxproj	
+++ b/Priority Queue/Tests/Tests.xcodeproj/project.pbxproj	
@@ -180,6 +180,7 @@
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = macosx;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -219,6 +220,7 @@
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = macosx;
 				SWIFT_OPTIMIZATION_LEVEL = "-Owholemodule";
+				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
 		};
@@ -230,7 +232,7 @@
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/../Frameworks @loader_path/../Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = swift.algorithm.club.Tests;
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -242,7 +244,7 @@
 				LD_RUNPATH_SEARCH_PATHS = "$(inherited) @executable_path/../Frameworks @loader_path/../Frameworks";
 				PRODUCT_BUNDLE_IDENTIFIER = swift.algorithm.club.Tests;
 				PRODUCT_NAME = "$(TARGET_NAME)";
-				SWIFT_VERSION = 3.0;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
 		};