diff --git a/crypto/fipsmodule/bn/asm/x86_64-gcc.c b/crypto/fipsmodule/bn/asm/x86_64-gcc.c
index bfd770f..12ffc3f 100644
--- a/crypto/fipsmodule/bn/asm/x86_64-gcc.c
+++ b/crypto/fipsmodule/bn/asm/x86_64-gcc.c
@@ -53,7 +53,8 @@
 #include <openssl/bn.h>
 
 // TODO(davidben): Get this file working on Windows x64.
-#if !defined(OPENSSL_NO_ASM) && defined(OPENSSL_X86_64) && defined(__GNUC__)
+#if !defined(OPENSSL_NO_ASM) && defined(OPENSSL_X86_64) && \
+    (defined(__GNUC__) || defined(__clang__))
 
 #include "../internal.h"
 
@@ -534,4 +535,4 @@
 #undef mul_add_c2
 #undef sqr_add_c2
 
-#endif  // !NO_ASM && X86_64 && __GNUC__
+#endif  // !NO_ASM && X86_64 && (__GNUC__ || __clang__)
diff --git a/crypto/fipsmodule/bn/div.c b/crypto/fipsmodule/bn/div.c
index 1bcff50..ded19e2 100644
--- a/crypto/fipsmodule/bn/div.c
+++ b/crypto/fipsmodule/bn/div.c
@@ -155,18 +155,18 @@
   //
   // These issues aren't specific to x86 and x86_64, so it might be worthwhile
   // to add more assembly language implementations.
-#if !defined(OPENSSL_NO_ASM) && defined(OPENSSL_X86) && defined(__GNUC__)
-  __asm__ volatile (
-    "divl %4"
-    : "=a"(*quotient_out), "=d"(*rem_out)
-    : "a"(n1), "d"(n0), "rm"(d0)
-    : "cc" );
-#elif !defined(OPENSSL_NO_ASM) && defined(OPENSSL_X86_64) && defined(__GNUC__)
-  __asm__ volatile (
-    "divq %4"
-    : "=a"(*quotient_out), "=d"(*rem_out)
-    : "a"(n1), "d"(n0), "rm"(d0)
-    : "cc" );
+#if !defined(OPENSSL_NO_ASM) && defined(OPENSSL_X86) && \
+    (defined(__GNUC__) || defined(__clang__))
+  __asm__ volatile("divl %4"
+                   : "=a"(*quotient_out), "=d"(*rem_out)
+                   : "a"(n1), "d"(n0), "rm"(d0)
+                   : "cc");
+#elif !defined(OPENSSL_NO_ASM) && defined(OPENSSL_X86_64) && \
+    (defined(__GNUC__) || defined(__clang__))
+  __asm__ volatile("divq %4"
+                   : "=a"(*quotient_out), "=d"(*rem_out)
+                   : "a"(n1), "d"(n0), "rm"(d0)
+                   : "cc");
 #else
 #if defined(BN_ULLONG)
   BN_ULLONG n = (((BN_ULLONG)n0) << BN_BITS2) | n1;
diff --git a/crypto/fipsmodule/bn/generic.c b/crypto/fipsmodule/bn/generic.c
index b70080f..8212409 100644
--- a/crypto/fipsmodule/bn/generic.c
+++ b/crypto/fipsmodule/bn/generic.c
@@ -64,7 +64,8 @@
 // This file has two other implementations: x86 assembly language in
 // asm/bn-586.pl and x86_64 inline assembly in asm/x86_64-gcc.c.
 #if defined(OPENSSL_NO_ASM) || \
-    !(defined(OPENSSL_X86) || (defined(OPENSSL_X86_64) && defined(__GNUC__)))
+    !(defined(OPENSSL_X86) ||  \
+      (defined(OPENSSL_X86_64) && (defined(__GNUC__) || defined(__clang__))))
 
 #ifdef BN_ULLONG
 #define mul_add(r, a, w, c)               \
diff --git a/crypto/fipsmodule/bn/internal.h b/crypto/fipsmodule/bn/internal.h
index ecd7d6c..4fca399 100644
--- a/crypto/fipsmodule/bn/internal.h
+++ b/crypto/fipsmodule/bn/internal.h
@@ -140,7 +140,7 @@
 
 #if defined(OPENSSL_64_BIT)
 
-#if !defined(_MSC_VER)
+#if !defined(_MSC_VER) || defined(__clang__)
 // MSVC doesn't support two-word integers on 64-bit.
 #define BN_ULLONG	uint128_t
 #endif
diff --git a/crypto/fipsmodule/ec/ec.c b/crypto/fipsmodule/ec/ec.c
index a39ca59..f432f79 100644
--- a/crypto/fipsmodule/ec/ec.c
+++ b/crypto/fipsmodule/ec/ec.c
@@ -212,13 +212,6 @@
     0xB7, 0x1E, 0x91, 0x38, 0x64, 0x09,
 };
 
-// MSan appears to have a bug that causes code to be miscompiled in opt mode.
-// While that is being looked at, don't run the uint128_t code under MSan.
-#if defined(OPENSSL_64_BIT) && !defined(OPENSSL_WINDOWS) && \
-    !defined(MEMORY_SANITIZER)
-#define BORINGSSL_USE_INT128_CODE
-#endif
-
 DEFINE_METHOD_FUNCTION(struct built_in_curves, OPENSSL_built_in_curves) {
   // 1.3.132.0.35
   static const uint8_t kOIDP521[] = {0x2b, 0x81, 0x04, 0x00, 0x23};
diff --git a/crypto/fipsmodule/ec/internal.h b/crypto/fipsmodule/ec/internal.h
index 39c9349..3536c78 100644
--- a/crypto/fipsmodule/ec/internal.h
+++ b/crypto/fipsmodule/ec/internal.h
@@ -79,6 +79,13 @@
 #endif
 
 
+// MSan appears to have a bug that causes code to be miscompiled in opt mode.
+// While that is being looked at, don't run the uint128_t code under MSan.
+#if defined(OPENSSL_64_BIT) && (!defined(_MSC_VER) || defined(__clang__)) && \
+    !defined(MEMORY_SANITIZER)
+#define BORINGSSL_USE_INT128_CODE
+#endif
+
 struct ec_method_st {
   int (*group_init)(EC_GROUP *);
   void (*group_finish)(EC_GROUP *);
diff --git a/crypto/fipsmodule/ec/p256-64.c b/crypto/fipsmodule/ec/p256-64.c
index f7d1ff1..ac038c0 100644
--- a/crypto/fipsmodule/ec/p256-64.c
+++ b/crypto/fipsmodule/ec/p256-64.c
@@ -21,8 +21,6 @@
 
 #include <openssl/base.h>
 
-#if defined(OPENSSL_64_BIT) && !defined(OPENSSL_WINDOWS)
-
 #include <openssl/bn.h>
 #include <openssl/ec.h>
 #include <openssl/err.h>
@@ -35,6 +33,8 @@
 #include "internal.h"
 
 
+#if defined(BORINGSSL_USE_INT128_CODE)
+
 // The underlying field. P256 operates over GF(2^256-2^224+2^192+2^96-1). We
 // can serialise an element of this field into 32 bytes. We call this an
 // felem_bytearray.
@@ -1705,4 +1705,4 @@
   out->field_decode = NULL;
 };
 
-#endif  // 64_BIT && !WINDOWS
+#endif  // BORINGSSL_USE_INT128_CODE