diff --git a/OnePasswordExtension.h b/OnePasswordExtension.h
index c5ec2f6..ee5c665 100644
--- a/OnePasswordExtension.h
+++ b/OnePasswordExtension.h
@@ -49,7 +49,7 @@ FOUNDATION_EXPORT NSInteger const AppExtensionErrorCodeUnexpectedData;
  Note that this returns YES if any app that supports the generic `org-appextension-feature-password-management` feature 
  is installed.
  */
-- (BOOL)isAppExtensionAvailable;
+- (BOOL)isAppExtensionAvailable NS_EXTENSION_UNAVAILABLE_IOS("Not available in an extension. Check if org-appextension-feature-password-management:// URL can be opened by the app.");
 
 /*!
  Called from your login page, this method will find all available logins for the given URLString. After the user selects