diff --git a/Format.xcodeproj/project.pbxproj b/Format.xcodeproj/project.pbxproj
index 23cd5a5..be00b1b 100644
--- a/Format.xcodeproj/project.pbxproj
+++ b/Format.xcodeproj/project.pbxproj
@@ -421,7 +421,7 @@
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SKIP_INSTALL = YES;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-				SWIFT_VERSION = 3.0;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -441,7 +441,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = com.roymarmelstein.Format;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 				SKIP_INSTALL = YES;
-				SWIFT_VERSION = 3.0;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
 		};
diff --git a/Format/NumberFormatter.swift b/Format/NumberFormatter.swift
index 87bd8b7..ed7a38d 100644
--- a/Format/NumberFormatter.swift
+++ b/Format/NumberFormatter.swift
@@ -90,7 +90,7 @@ open class NumberFormat {
             } else if formatter.modifier == NumberFormatterSpellOutKey {
                 formattedString = nsFormatter.string(from: number)
             } else if formatter.modifier == NumberFormatterDistanceKey {
-                let distance = number as CLLocationDistance
+                let distance = number as! CLLocationDistance
                 formattedString = distanceFormatter.string(fromDistance: distance)
             }
         }