diff --git a/Help/variable/CMAKE_MACOSX_BUNDLE.rst b/Help/variable/CMAKE_MACOSX_BUNDLE.rst
index 0badaf0dae..43ddff517a 100644
--- a/Help/variable/CMAKE_MACOSX_BUNDLE.rst
+++ b/Help/variable/CMAKE_MACOSX_BUNDLE.rst
@@ -5,3 +5,6 @@ Default value for :prop_tgt:`MACOSX_BUNDLE` of targets.
 
 This variable is used to initialize the :prop_tgt:`MACOSX_BUNDLE` property on
 all the targets.  See that target property for additional information.
+
+This variable is set to ``ON`` by default if :variable:`CMAKE_SYSTEM_NAME`
+equals to :ref:`iOS, tvOS or watchOS <Cross Compiling for iOS, tvOS, or watchOS>`.