diff --git a/.github/workflows/windows.yml b/.github/workflows/windows.yml
index 1c41e2866..769a95ace 100644
--- a/.github/workflows/windows.yml
+++ b/.github/workflows/windows.yml
@@ -20,7 +20,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [windows-2025, windows-2022]
+        os: [windows-2025, windows-2022, windows-11-arm]
     runs-on: ${{ matrix.os }}
     steps:
       - name: Install dependencies
@@ -41,4 +41,6 @@ jobs:
           # CB_CMAKE_BUILD_TYPE: Release
           CB_CMAKE_BUILD_TYPE: RelWithDebInfo
           CB_NUMBER_OF_JOBS: 2
+          # No OpenSSL ASM exists for Window-11=arm.
+          CB_OPENSSL_NO_ASM: ${{ matrix.os == 'windows-11-arm' && '1' || '' }}
         run: ruby ./bin/build-tests.rb
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 28535d653..95c7ac790 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -32,6 +32,12 @@ if(WIN32)
   message(STATUS "Windows SDK: ${CMAKE_VS_WINDOWS_TARGET_PLATFORM_VERSION}")
 endif()
 
+# This disables Microsoft’s C++ overloads for _Interlocked* and fixes the ARM64 build.
+if (WIN32 AND CMAKE_SIZEOF_VOID_P EQUAL 8 AND CMAKE_SYSTEM_PROCESSOR MATCHES "ARM64")
+    message(STATUS "Applying WinBase Interlocked macro for Windows ARM64")
+    add_compile_definitions(MICROSOFT_WINDOWS_WINBASE_H_DEFINE_INTERLOCKED_CPLUSPLUS_OVERLOADS=0)
+endif()
+
 include(cmake/TarballRelease.cmake OPTIONAL)
 
 include(cmake/PreventInSourceBuilds.cmake)
diff --git a/bin/build-tests.rb b/bin/build-tests.rb
index 4224aef92..6fc5260cb 100755
--- a/bin/build-tests.rb
+++ b/bin/build-tests.rb
@@ -88,6 +88,11 @@ def run(*args)
   CB_CMAKE_EXTRAS << "-DENABLE_SANITIZER_MEMORY=ON"
 end
 
+# No OpenSSLASM exists for Window ARM64
+if ENV["CB_OPENSSL_NO_ASM"] == "1"
+  CB_CMAKE_EXTRAS << "-DOPENSSL_NO_ASM=1"
+end
+
 BUILD_DIR = if CB_SANITIZER.empty?
               File.join(PROJECT_ROOT, "cmake-build-tests")
             else
diff --git a/core/platform/random.cc b/core/platform/random.cc
index d3bf40215..9f27cb019 100644
--- a/core/platform/random.cc
+++ b/core/platform/random.cc
@@ -25,7 +25,7 @@
 #include <mutex>
 #include <system_error>
 
-#ifdef WIN32
+#ifdef _WIN32
 // We need to include windows.h _before_ wincrypt.h
 #ifndef WIN32_LEAN_AND_MEAN
 #define WIN32_LEAN_AND_MEAN