1 files changed, 13 insertions, 1 deletions
diff --git a/Firebase/Auth/Source/FIRAuthAppDelegateProxy.m b/Firebase/Auth/Source/FIRAuthAppDelegateProxy.m
index f13e94f..3289b4e 100644
--- a/Firebase/Auth/Source/FIRAuthAppDelegateProxy.m
+++ b/Firebase/Auth/Source/FIRAuthAppDelegateProxy.m
@@ -16,6 +16,8 @@
 
 #import "FIRAuthAppDelegateProxy.h"
 
+#import <FirebaseCore/FIRAppEnvironmentUtil.h>
+
 #import <objc/runtime.h>
 
 NS_ASSUME_NONNULL_BEGIN
@@ -200,8 +202,18 @@ static BOOL isIOS9orLater() {
 + (nullable instancetype)sharedInstance {
   static dispatch_once_t onceToken;
   static FIRAuthAppDelegateProxy *_Nullable sharedInstance;
+  // iOS App extensions should not call [UIApplication sharedApplication], even if UIApplication
+  // responds to it.
+  static Class applicationClass = nil;
+  if (![FIRAppEnvironmentUtil isAppExtension]) {
+    Class cls = NSClassFromString(@"UIApplication");
+    if (cls && [cls respondsToSelector:NSSelectorFromString(@"sharedApplication")]) {
+      applicationClass = cls;
+    }
+  }
+  UIApplication *application = [applicationClass sharedApplication];
   dispatch_once(&onceToken, ^{
-    sharedInstance = [[self alloc] initWithApplication:[UIApplication sharedApplication]];
+    sharedInstance = [[self alloc] initWithApplication:application];
   });
   return sharedInstance;
 }