diff --git a/scripts/build.mjs b/scripts/build.mjs
index 5ede415f9e..d30ad680bf 100755
--- a/scripts/build.mjs
+++ b/scripts/build.mjs
@@ -85,9 +85,13 @@ async function build(args) {
     generateOptions["--toolchain"] = toolchainPath;
   }
 
-  // Windows ARM64: log detection (compiler is selected by CMake/toolchain)
+  // Windows ARM64: cmake.exe is x64 so the OS reports PROCESSOR_ARCHITECTURE=AMD64.
+  // Override CMAKE_SYSTEM_PROCESSOR so cmake detects ARM64 correctly.
   if (isWindowsARM64) {
     console.log("Windows ARM64 detected");
+    if (!generateOptions["-DCMAKE_SYSTEM_PROCESSOR"]) {
+      generateOptions["-DCMAKE_SYSTEM_PROCESSOR"] = "ARM64";
+    }
   }
 
   const generateArgs = Object.entries(generateOptions).flatMap(([flag, value]) =>