diff --git a/Sources/Pageboy.xcodeproj/project.pbxproj b/Sources/Pageboy.xcodeproj/project.pbxproj
index 3bb42973..fe2a67e8 100644
--- a/Sources/Pageboy.xcodeproj/project.pbxproj
+++ b/Sources/Pageboy.xcodeproj/project.pbxproj
@@ -686,7 +686,7 @@
 				PRODUCT_NAME = Pageboy;
 				SKIP_INSTALL = YES;
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
-				SWIFT_VERSION = 4.2;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Debug;
 		};
@@ -704,7 +704,7 @@
 				PRODUCT_BUNDLE_IDENTIFIER = com.uias.Pageboy;
 				PRODUCT_NAME = Pageboy;
 				SKIP_INSTALL = YES;
-				SWIFT_VERSION = 4.2;
+				SWIFT_VERSION = 4.0;
 			};
 			name = Release;
 		};
diff --git a/Sources/Pageboy/PageboyViewController+Management.swift b/Sources/Pageboy/PageboyViewController+Management.swift
index 1cfddd50..4876dbb6 100644
--- a/Sources/Pageboy/PageboyViewController+Management.swift
+++ b/Sources/Pageboy/PageboyViewController+Management.swift
@@ -164,15 +164,27 @@ internal extension PageboyViewController {
         pageViewController.dataSource = self
         self.pageViewController = pageViewController
         
+        #if swift(>=4.2)
         addChild(pageViewController)
+        #else
+        addChildViewController(pageViewController)
+        #endif
         if let existingZIndex = existingZIndex {
             view.insertSubview(pageViewController.view, at: existingZIndex)
         } else {
             view.addSubview(pageViewController.view)
+            #if swift(>=4.2)
             view.sendSubviewToBack(pageViewController.view)
+            #else
+            view.sendSubview(toBack: pageViewController.view)
+            #endif
         }
         pageViewController.view.pinToSuperviewEdges()
+        #if swift(>=4.2)
         pageViewController.didMove(toParent: self)
+        #else
+        pageViewController.didMove(toParentViewController: self)
+        #endif
         
         pageViewController.scrollView?.delegate = self
         pageViewController.view.backgroundColor = .clear
@@ -185,7 +197,11 @@ internal extension PageboyViewController {
     
     private func destroyCurrentPageViewController() {
         pageViewController?.view.removeFromSuperview()
+        #if swift(>=4.2)
         pageViewController?.removeFromParent()
+        #else
+        pageViewController?.removeFromParentViewController()
+        #endif
         pageViewController = nil
     }
     
@@ -197,6 +213,7 @@ internal extension PageboyViewController {
         setUpPageViewController(reloadViewControllers: false)
     }
     
+    #if swift(>=4.2)
     /// The options to be passed to a UIPageViewController instance.
     internal var pageViewControllerOptions: [UIPageViewController.OptionsKey: Any]? {
         var options = [UIPageViewController.OptionsKey: Any]()
@@ -210,6 +227,21 @@ internal extension PageboyViewController {
         }
         return options
     }
+    #else
+    /// The options to be passed to a UIPageViewController instance.
+    internal var pageViewControllerOptions: [String: Any]? {
+        var options = [String: Any]()
+        
+        if interPageSpacing > 0.0 {
+            options[UIPageViewControllerOptionInterPageSpacingKey] = interPageSpacing
+        }
+        
+        guard options.count > 0 else {
+            return nil
+        }
+        return options
+    }
+    #endif
 }
 
 // MARK: - UIPageViewControllerDataSource, PageboyViewControllerDataSource
diff --git a/Sources/Pageboy/Transitioning/PageboyViewController+Transitioning.swift b/Sources/Pageboy/Transitioning/PageboyViewController+Transitioning.swift
index 94278fc7..9533f08c 100644
--- a/Sources/Pageboy/Transitioning/PageboyViewController+Transitioning.swift
+++ b/Sources/Pageboy/Transitioning/PageboyViewController+Transitioning.swift
@@ -58,7 +58,11 @@ internal extension PageboyViewController {
 
         let displayLink = CADisplayLink(target: self, selector: #selector(displayLinkDidTick))
         displayLink.isPaused = true
+        #if swift(>=4.2)
         displayLink.add(to: .main, forMode: .common)
+        #else
+        displayLink.add(to: .main, forMode: .commonModes)
+        #endif
         transitionDisplayLink = displayLink
     }
     
@@ -156,6 +160,10 @@ internal extension PageboyViewController.Transition {
     
     func configure(transition: inout CATransition) {
         transition.duration = duration
+        #if swift(>=4.2)
         transition.type = CATransitionType(rawValue: style.rawValue)
+        #else
+        transition.type = style.rawValue
+        #endif
     }
 }
diff --git a/Sources/Pageboy/Transitioning/TransitionOperation+Action.swift b/Sources/Pageboy/Transitioning/TransitionOperation+Action.swift
index a1f97a10..8ca3bbcb 100644
--- a/Sources/Pageboy/Transitioning/TransitionOperation+Action.swift
+++ b/Sources/Pageboy/Transitioning/TransitionOperation+Action.swift
@@ -30,6 +30,7 @@ internal extension TransitionOperation {
 
 internal extension TransitionOperation.Action {
     
+    #if swift(>=4.2)
     /// Animation sub-type for the action.
     var transitionSubType: CATransitionSubtype {
         switch orientation {
@@ -53,4 +54,29 @@ internal extension TransitionOperation.Action {
             }
         }
     }
+    #else
+    /// Animation sub-type for the action.
+    var transitionSubType: String {
+        switch orientation {
+            
+        case .horizontal:
+            switch semanticDirection {
+                
+            case .reverse:
+                return kCATransitionFromLeft
+            default:
+                return kCATransitionFromRight
+            }
+            
+        case .vertical:
+            switch semanticDirection {
+                
+            case .reverse:
+                return kCATransitionFromBottom
+            default:
+                return kCATransitionFromTop
+            }
+        }
+    }
+    #endif
 }
diff --git a/Sources/Pageboy/Transitioning/TransitionOperation.swift b/Sources/Pageboy/Transitioning/TransitionOperation.swift
index 6eb0328f..00ed4309 100644
--- a/Sources/Pageboy/Transitioning/TransitionOperation.swift
+++ b/Sources/Pageboy/Transitioning/TransitionOperation.swift
@@ -86,7 +86,11 @@ internal class TransitionOperation: NSObject, CAAnimationDelegate {
         animation.endProgress = 1.0
         transition.configure(transition: &animation)
         animation.subtype = action.transitionSubType
+        #if swift(>=4.2)
         animation.fillMode = .backwards
+        #else
+        animation.fillMode = kCAFillModeBackwards
+        #endif
         self.animation = animation
         
         super.init()