diff --git a/src/int128_struct_impl.h b/src/int128_struct_impl.h
index f92b04b116..caa5413b06 100644
--- a/src/int128_struct_impl.h
+++ b/src/int128_struct_impl.h
@@ -3,7 +3,7 @@
 
 #include "int128.h"
 
-#if defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64)) /* MSVC */
+#if defined(_MSC_VER) && defined(_WIN64) && (defined(_M_X64) || defined(_M_ARM64)) /* 64-bit MSVC */
 #    if defined(_M_X64)
 /* On x84_64 MSVC, use native __(u)mul128 for 64x64->128 multiplications. */
 #        include <intrin.h>
diff --git a/src/util.h b/src/util.h
index 9292893c03..7145070009 100644
--- a/src/util.h
+++ b/src/util.h
@@ -244,7 +244,7 @@ static SECP256K1_INLINE void secp256k1_int_cmov(int *r, const int *a, int flag)
 #elif defined(UINT128_MAX) || defined(__SIZEOF_INT128__)
 # define SECP256K1_WIDEMUL_INT128 1
 # define SECP256K1_INT128_NATIVE 1
-#elif defined(_MSC_VER) && (defined(_M_X64) || defined(_M_ARM64))
+#elif defined(_MSC_VER) && defined(_WIN64) && (defined(_M_X64) || defined(_M_ARM64))
 # define SECP256K1_WIDEMUL_INT128 1
 # define SECP256K1_INT128_STRUCT 1
 #else