diff --git a/cmake/external/xnnpack.cmake b/cmake/external/xnnpack.cmake
index 9519e4e6a779..c3cc92b2300b 100644
--- a/cmake/external/xnnpack.cmake
+++ b/cmake/external/xnnpack.cmake
@@ -80,6 +80,7 @@ MESSAGE(STATUS "Building for ORT_TARGET_PROCESSOR: ${ORT_TARGET_PROCESSOR}")
 # KleidiAI is only used in Arm64 platform and not supported by MSVC, the details can be seen in
 # https://github.com/google/XNNPACK/blob/3b3f7b8a6668f6ab3b6ce33b9f1d1fce971549d1/CMakeLists.txt#L206C82-L206C117
 if(ORT_TARGET_PROCESSOR MATCHES "^arm64.*" AND NOT CMAKE_C_COMPILER_ID STREQUAL "MSVC")
+  set(CMAKE_SYSTEM_PROCESSOR aarch64)
   FetchContent_Declare(kleidiai URL ${DEP_URL_kleidiai} URL_HASH SHA1=${DEP_SHA1_kleidiai})
   onnxruntime_fetchcontent_makeavailable(kleidiai)
   set(KLEIDIAI_SOURCE_DIR ${kleidiai_SOURCE_DIR})