diff --git a/Classes/ios/UIBarButtonItem+FlatUI.m b/Classes/ios/UIBarButtonItem+FlatUI.m
index fa13521..2d8cb95 100644
--- a/Classes/ios/UIBarButtonItem+FlatUI.m
+++ b/Classes/ios/UIBarButtonItem+FlatUI.m
@@ -27,11 +27,30 @@ + (void) configureFlatButtonsWithColor:(UIColor *) color
                       highlightedColor:(UIColor *)highlightedColor
                           cornerRadius:(CGFloat) cornerRadius
                        whenContainedIn:(Class <UIAppearanceContainer>)containerClass, ... {
-  va_list vl;
-  va_start(vl, containerClass);
-  id appearance = [UIBarButtonItem appearanceWhenContainedIn:containerClass, nil];
-  va_end(vl);
-  [UIBarButtonItem configureItemOrProxy:appearance forFlatButtonWithColor:color highlightedColor:highlightedColor cornerRadius:cornerRadius];
+    NSMutableArray *containerClasses = [NSMutableArray array];
+        if (containerClass) {
+            [containerClasses addObject:containerClass];
+            
+            va_list vl;
+            va_start(vl, containerClass);
+            Class arg;
+            while ((arg = va_arg(vl, Class))) {
+                [containerClasses addObject:arg];
+            }
+            va_end(vl);
+        }
+
+        id appearance;
+        if (@available(iOS 9.0, *)) {
+            appearance = [UIBarButtonItem appearanceWhenContainedInInstancesOfClasses:containerClasses];
+        } else {
+    #pragma clang diagnostic push
+    #pragma clang diagnostic ignored "-Wdeprecated-declarations"
+            appearance = [UIBarButtonItem appearanceWhenContainedIn:containerClass, nil];
+    #pragma clang diagnostic pop
+        }
+
+        [UIBarButtonItem configureItemOrProxy:appearance forFlatButtonWithColor:color highlightedColor:highlightedColor cornerRadius:cornerRadius];
 }
 
 // only used pre-ios7