diff --git a/faiss/impl/platform_macros.h b/faiss/impl/platform_macros.h
index 3e9716b06f..8d069995b3 100644
--- a/faiss/impl/platform_macros.h
+++ b/faiss/impl/platform_macros.h
@@ -39,6 +39,7 @@
 // redefine the GCC intrinsics with Windows equivalents
 
 #include <intrin.h>
+#include <limits.h>
 
 #ifndef __clang__
 inline int __builtin_ctzll(uint64_t x) {
@@ -59,7 +60,16 @@ inline int __builtin_ctz(unsigned long x) {
 
 #ifndef __clang__
 inline int __builtin_clzll(uint64_t x) {
+#if defined(_M_X64) || defined(__x86_64__)
     return (int)__lzcnt64(x);
+#elif defined(_M_ARM64)
+    unsigned long index;
+    int count = sizeof(uint64_t) * CHAR_BIT;
+    if (_BitScanReverse64(&index, x)) {
+        count = count - 1 - index;
+    }
+    return count;
+#endif
 }
 #endif