diff --git a/FSImageViewer/FSBasicImage.h b/FSImageViewer/FSBasicImage.h
index c6b4a7b..3735ec7 100644
--- a/FSImageViewer/FSBasicImage.h
+++ b/FSImageViewer/FSBasicImage.h
@@ -29,16 +29,16 @@
 
 /// @param URL remote image URL
 /// @param name title of the image
-- (instancetype)initWithImageURL:(NSURL *)URL name:(NSString *)name;
+- (instancetype _Nonnull)initWithImageURL:(NSURL * _Nonnull)URL name:(NSString * _Nullable)name;
 
 /// @param URL remote image URL
-- (instancetype)initWithImageURL:(NSURL *)URL;
+- (instancetype _Nonnull)initWithImageURL:(NSURL * _Nonnull)URL;
 
 /// @param image an UIImage representation of the image
-- (instancetype)initWithImage:(UIImage *)image;
+- (instancetype _Nonnull)initWithImage:(UIImage * _Nonnull)image;
 
 /// @param image an UIImage representation of the image
 /// @param name title of the image
-- (instancetype)initWithImage:(UIImage *)image name:(NSString *)name;
+- (instancetype _Nonnull)initWithImage:(UIImage * _Nonnull)image name:(NSString * _Nullable)name;
 
 @end
diff --git a/FSImageViewer/FSBasicImageSource.h b/FSImageViewer/FSBasicImageSource.h
index df5e125..7eff79c 100644
--- a/FSImageViewer/FSBasicImageSource.h
+++ b/FSImageViewer/FSBasicImageSource.h
@@ -29,6 +29,6 @@
 @interface FSBasicImageSource : NSObject<FSImageSource>
 
 /// @param images array of FSImage objects
-- (instancetype)initWithImages:(NSArray<id <FSImage>>*)images;
+- (instancetype _Nonnull)initWithImages:(NSArray<id <FSImage>>* _Nonnull)images;
 
 @end
diff --git a/FSImageViewer/FSBasicImageSource.m b/FSImageViewer/FSBasicImageSource.m
index dfbdfee..e1fac2c 100644
--- a/FSImageViewer/FSBasicImageSource.m
+++ b/FSImageViewer/FSBasicImageSource.m
@@ -29,7 +29,7 @@ @implementation FSBasicImageSource
 @synthesize images = _images;
 @synthesize numberOfImages = _numberOfImages;
 
-- (instancetype)initWithImages:(NSArray<id <FSImage>>*)images{
+- (instancetype _Nonnull)initWithImages:(NSArray<id <FSImage>>* _Nonnull)images{
 	
 	if (self = [super init]) {
         _images = images;
diff --git a/FSImageViewer/FSImageLoader.h b/FSImageViewer/FSImageLoader.h
index 5e05311..8c5239b 100644
--- a/FSImageViewer/FSImageLoader.h
+++ b/FSImageViewer/FSImageLoader.h
@@ -24,6 +24,8 @@
 
 #import <UIKit/UIKit.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 /// Download remote images with AFNetworking
 @interface FSImageLoader : NSObject
 
@@ -36,7 +38,7 @@
 /// Download remote images from url
 /// @param url remote image url
 /// @param imageBlock block for image or error
-- (void)loadImageForURL:(NSURL *)url progress:(void (^)(float progress))progress image:(void (^)(UIImage *image, NSError *error))imageBlock;
+- (void)loadImageForURL:(NSURL * _Nonnull)url progress:(void (^)(float progress))progress image:(void (^)(UIImage * __nullable image, NSError * __nullable error))imageBlock;
 
 /// Cancel all image requests
 - (void)cancelAllRequests;
@@ -45,4 +47,6 @@
 /// @param url remote image url
 - (void)cancelRequestForUrl:(NSURL *)url;
 
+NS_ASSUME_NONNULL_END
+
 @end
\ No newline at end of file
diff --git a/FSImageViewer/FSImageViewerViewController.h b/FSImageViewer/FSImageViewerViewController.h
index 3a39b25..2969c62 100644
--- a/FSImageViewer/FSImageViewerViewController.h
+++ b/FSImageViewer/FSImageViewerViewController.h
@@ -26,6 +26,8 @@
 #import "FSImageSource.h"
 #import "FSTitleView.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @class FSImageViewerViewController;
 
 // Optional Delegate for getting current presented image index.
@@ -55,16 +57,16 @@
 @property(strong, nonatomic, readonly) id <FSImageSource> imageSource;
 
 /// Title
-@property(strong, nonatomic) UIView<FSTitleView>* titleView;
+@property(strong, nonatomic, nullable) UIView<FSTitleView>* titleView;
 
 /// Optional Delegate
-@property(weak, nonatomic) id<FSImageViewerViewControllerDelegate> delegate;
+@property(weak, nonatomic, nullable) id<FSImageViewerViewControllerDelegate> delegate;
 
 /// FSImageView array
-@property(strong, nonatomic) NSMutableArray *imageViews;
+@property(strong, nonatomic, nullable) NSMutableArray *imageViews;
 
 /// Main scrollView
-@property(strong, nonatomic) UIScrollView *scrollView;
+@property(strong, nonatomic, nullable) UIScrollView *scrollView;
 
 /// Display a "x of y" images in the navigation title - Default is YES
 @property(assign, nonatomic) BOOL showNumberOfItemsInTitle;
@@ -76,19 +78,19 @@
 @property(assign, nonatomic, getter = isRotationEnabled) BOOL rotationEnabled;
 
 /// Override the background color when overlay is hidden - Default is black
-@property(strong, nonatomic) UIColor *backgroundColorHidden;
+@property(strong, nonatomic, nullable) UIColor *backgroundColorHidden;
 
 /// Override the background color when overlay is visible - Default is white
-@property(strong, nonatomic) UIColor *backgroundColorVisible;
+@property(strong, nonatomic, nullable) UIColor *backgroundColorVisible;
 
 /// Override the progressView color when overlay is hidden - Default is white
-@property(strong, nonatomic) UIColor *progressColorHidden;
+@property(strong, nonatomic, nullable) UIColor *progressColorHidden;
 
 /// Override the progressView color when overlay is visible - Default is darkGrayColor
-@property(strong, nonatomic) UIColor *progressColorVisible;
+@property(strong, nonatomic, nullable) UIColor *progressColorVisible;
 
 /// Used to add additional items to the "share" button
-@property(strong, nonatomic) NSArray* applicationActivities;
+@property(strong, nonatomic, nullable) NSArray* applicationActivities;
 
 /// Current index of the image displayed
 /// @return current index of the image displayed
@@ -99,4 +101,6 @@
 /// @param animated should the movevement animated
 - (void)moveToImageAtIndex:(NSInteger)index animated:(BOOL)animated;
 
+NS_ASSUME_NONNULL_END
+
 @end
\ No newline at end of file
diff --git a/FSImageViewer/FSPlaceholderImages.h b/FSImageViewer/FSPlaceholderImages.h
index 38b9db7..92a80d5 100644
--- a/FSImageViewer/FSPlaceholderImages.h
+++ b/FSImageViewer/FSPlaceholderImages.h
@@ -26,6 +26,6 @@
 
 @interface FSPlaceholderImages : NSObject
 
-+ (UIImage *)errorImage;
++ (UIImage * _Nonnull)errorImage;
 
 @end
\ No newline at end of file