diff --git a/ec/native/curve25519_stubs.c b/ec/native/curve25519_stubs.c
index 283a453a..e5fdab90 100644
--- a/ec/native/curve25519_stubs.c
+++ b/ec/native/curve25519_stubs.c
@@ -1,6 +1,9 @@
 #include "mirage_crypto.h"
 
-#ifdef ARCH_64BIT
+/* Microsoft compiler does not support 128-bit integers. Drop down to
+ * 32-bit for MSVC.
+ */
+#if defined(ARCH_64BIT) && !defined(_MSC_VER)
 #include "curve25519_64.h"
 #define WORD uint64_t
 #define LIMBS 5
diff --git a/ec/native/np224_stubs.c b/ec/native/np224_stubs.c
index fe64b5b4..dc29afea 100644
--- a/ec/native/np224_stubs.c
+++ b/ec/native/np224_stubs.c
@@ -1,6 +1,9 @@
 #include "mirage_crypto.h"
 
-#ifdef ARCH_64BIT
+/* Microsoft compiler does not support 128-bit integers. Drop down to
+ * 32-bit for MSVC.
+ */
+#if defined(ARCH_64BIT) && !defined(_MSC_VER)
 #include "np224_64.h"
 #define LIMBS 4
 #define WORD uint64_t
diff --git a/ec/native/np256_stubs.c b/ec/native/np256_stubs.c
index cd4aa30d..4da63dbc 100644
--- a/ec/native/np256_stubs.c
+++ b/ec/native/np256_stubs.c
@@ -1,6 +1,9 @@
 #include "mirage_crypto.h"
 
-#ifdef ARCH_64BIT
+/* Microsoft compiler does not support 128-bit integers. Drop down to
+ * 32-bit for MSVC.
+ */
+#if defined(ARCH_64BIT) && !defined(_MSC_VER)
 #include "np256_64.h"
 #define LIMBS 4
 #define WORD uint64_t
diff --git a/ec/native/np384_stubs.c b/ec/native/np384_stubs.c
index c1abd4e5..97893e06 100644
--- a/ec/native/np384_stubs.c
+++ b/ec/native/np384_stubs.c
@@ -1,6 +1,9 @@
 #include "mirage_crypto.h"
 
-#ifdef ARCH_64BIT
+/* Microsoft compiler does not support 128-bit integers. Drop down to
+ * 32-bit for MSVC.
+ */
+#if defined(ARCH_64BIT) && !defined(_MSC_VER)
 #include "np384_64.h"
 #define LIMBS 6
 #define WORD uint64_t
diff --git a/ec/native/np521_stubs.c b/ec/native/np521_stubs.c
index aaa8bf5a..39439309 100644
--- a/ec/native/np521_stubs.c
+++ b/ec/native/np521_stubs.c
@@ -1,6 +1,9 @@
 #include "mirage_crypto.h"
 
-#ifdef ARCH_64BIT
+/* Microsoft compiler does not support 128-bit integers. Drop down to
+ * 32-bit for MSVC.
+ */
+#if defined(ARCH_64BIT) && !defined(_MSC_VER)
 #include "np521_64.h"
 #define LIMBS 9
 #define WORD uint64_t
diff --git a/ec/native/p224_stubs.c b/ec/native/p224_stubs.c
index 0a5da891..2924901e 100644
--- a/ec/native/p224_stubs.c
+++ b/ec/native/p224_stubs.c
@@ -1,6 +1,9 @@
 #include "mirage_crypto.h"
 
-#ifdef ARCH_64BIT
+/* Microsoft compiler does not support 128-bit integers. Drop down to
+ * 32-bit for MSVC.
+ */
+#if defined(ARCH_64BIT) && !defined(_MSC_VER)
 #include "p224_64.h"
 #define LIMBS 4
 #define WORD uint64_t
diff --git a/ec/native/p256_stubs.c b/ec/native/p256_stubs.c
index 7dc2d927..ac611b6b 100644
--- a/ec/native/p256_stubs.c
+++ b/ec/native/p256_stubs.c
@@ -1,6 +1,9 @@
 #include "mirage_crypto.h"
 
-#ifdef ARCH_64BIT
+/* Microsoft compiler does not support 128-bit integers. Drop down to
+ * 32-bit for MSVC.
+ */
+#if defined(ARCH_64BIT) && !defined(_MSC_VER)
 #include "p256_64.h"
 #define LIMBS 4
 #define WORD uint64_t
diff --git a/ec/native/p384_stubs.c b/ec/native/p384_stubs.c
index 2b2efd2a..fec2e485 100644
--- a/ec/native/p384_stubs.c
+++ b/ec/native/p384_stubs.c
@@ -1,6 +1,9 @@
 #include "mirage_crypto.h"
 
-#ifdef ARCH_64BIT
+/* Microsoft compiler does not support 128-bit integers. Drop down to
+ * 32-bit for MSVC.
+ */
+#if defined(ARCH_64BIT) && !defined(_MSC_VER)
 #include "p384_64.h"
 #define LIMBS 6
 #define WORD uint64_t
diff --git a/ec/native/p521_stubs.c b/ec/native/p521_stubs.c
index e8d6764d..294aa058 100644
--- a/ec/native/p521_stubs.c
+++ b/ec/native/p521_stubs.c
@@ -1,6 +1,9 @@
 #include "mirage_crypto.h"
 
-#ifdef ARCH_64BIT
+/* Microsoft compiler does not support 128-bit integers. Drop down to
+ * 32-bit for MSVC.
+ */
+#if defined(ARCH_64BIT) && !defined(_MSC_VER)
 #include "p521_64.h"
 #define LIMBS 9
 #define WORD uint64_t
diff --git a/src/native/ghash_ctmul.c b/src/native/ghash_ctmul.c
index ebd6589d..32b7f9f8 100644
--- a/src/native/ghash_ctmul.c
+++ b/src/native/ghash_ctmul.c
@@ -39,6 +39,9 @@
 #include "mirage_crypto.h"
 #include <string.h>
 
+/* Microsoft compiler does not support 128-bit integers. Drop down to
+ * 32-bit for MSVC.
+ */
 #if defined (__i386__) || defined (__arm__) || defined(_MSC_VER)
 
 /*