diff --git a/Shortest Path (Unweighted)/ShortestPath.playground/Pages/Shortest path example.xcplaygroundpage/Contents.swift b/Shortest Path (Unweighted)/ShortestPath.playground/Pages/Shortest path example.xcplaygroundpage/Contents.swift
index 9f2eda4f3..2404f5b8c 100644
--- a/Shortest Path (Unweighted)/ShortestPath.playground/Pages/Shortest path example.xcplaygroundpage/Contents.swift	
+++ b/Shortest Path (Unweighted)/ShortestPath.playground/Pages/Shortest path example.xcplaygroundpage/Contents.swift	
@@ -1,3 +1,8 @@
+// last checked with Xcode 9.0b4
+#if swift(>=4.0)
+print("Hello, Swift 4!")
+#endif
+
 func breadthFirstSearchShortestPath(graph: Graph, source: Node) -> Graph {
   let shortestPathGraph = graph.duplicate()
 
diff --git a/Shortest Path (Unweighted)/Tests/ShortestPathTests.swift b/Shortest Path (Unweighted)/Tests/ShortestPathTests.swift
index 71b9f88ab..4d79eeaa7 100644
--- a/Shortest Path (Unweighted)/Tests/ShortestPathTests.swift	
+++ b/Shortest Path (Unweighted)/Tests/ShortestPathTests.swift	
@@ -1,6 +1,13 @@
 import XCTest
 
 class ShortestPathTests: XCTestCase {
+  
+  func testSwift4() {
+    // last checked with Xcode 9.0b4
+    #if swift(>=4.0)
+      print("Hello, Swift 4!")
+    #endif
+  }
 
   func testShortestPathWhenGivenTree() {
     let tree = Graph()
diff --git a/Shortest Path (Unweighted)/Tests/Tests.xcodeproj/project.pbxproj b/Shortest Path (Unweighted)/Tests/Tests.xcodeproj/project.pbxproj
index f1744fcf1..b601a1665 100644
--- a/Shortest Path (Unweighted)/Tests/Tests.xcodeproj/project.pbxproj	
+++ b/Shortest Path (Unweighted)/Tests/Tests.xcodeproj/project.pbxproj	
@@ -182,6 +182,7 @@
 				ONLY_ACTIVE_ARCH = YES;
 				SDKROOT = macosx;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -218,6 +219,7 @@
 				MACOSX_DEPLOYMENT_TARGET = 10.11;
 				MTL_ENABLE_DEBUG_INFO = NO;
 				SDKROOT = macosx;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
 		};
@@ -231,7 +233,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = swift.algorithm.club.Tests;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-				SWIFT_VERSION = 3.0;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -244,7 +246,7 @@
 				LD_RUNPATH_SEARCH_PATHS = "$(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;
 		};