diff --git a/conans/client/build/cmake_flags.py b/conans/client/build/cmake_flags.py
index 9a76bbb9ded..f8ed3a83e2d 100644
--- a/conans/client/build/cmake_flags.py
+++ b/conans/client/build/cmake_flags.py
@@ -1,4 +1,5 @@
 import os
+import platform
 from collections import OrderedDict
 
 from conans.client import tools
@@ -294,9 +295,12 @@ def get_definitions(self):
         definitions.update(build_type_definition(self._forced_build_type, build_type,
                                                  self._generator, self._output))
 
-        if str(os_) == "Macos":
-            if arch == "x86":
-                definitions["CMAKE_OSX_ARCHITECTURES"] = "i386"
+        if tools.is_apple_os(os_):
+            definitions["CMAKE_OSX_ARCHITECTURES"] = tools.to_apple_arch(arch)
+            # xcrun is only available on macOS, otherwise it's cross-compiling and it needs to be
+            # set within CMake toolchain
+            if platform.system() == "Darwin":
+                definitions["CMAKE_OSX_SYSROOT"] = tools.XCRun(self._conanfile.settings).sdk_path
 
         definitions.update(self._cmake_cross_build_defines())
         definitions.update(self._get_cpp_standard_vars())
diff --git a/conans/test/unittests/client/build/cmake_test.py b/conans/test/unittests/client/build/cmake_test.py
index dc2fc6acba3..9c8a961b75a 100644
--- a/conans/test/unittests/client/build/cmake_test.py
+++ b/conans/test/unittests/client/build/cmake_test.py
@@ -1307,8 +1307,9 @@ def install_definitions_test(self):
                            ("iOS", "7.0",),
                            ("watchOS", "4.0",),
                            ("tvOS", "11.0",)])
-    @mock.patch('platform.system', return_value="Macos")
-    def test_cmake_system_version_osx(self, the_os, os_version, _):
+    @mock.patch("platform.system", return_value="Darwin")
+    @mock.patch("conans.client.tools.apple.XCRun.sdk_path", return_value='/opt')
+    def test_cmake_system_version_osx(self, the_os, os_version, _, __):
         settings = Settings.loads(get_default_settings_yml())
         settings.os = the_os