diff --git a/build.rs b/build.rs
--- a/build.rs
+++ b/build.rs
@@ -346,7 +346,27 @@
     // we want to optimize for minimizing the build tools required: No Perl,
     // no nasm, etc.
     let generated_dir = if !is_git {
-        c_root_dir.join(PREGENERATED)
+        let pregenerated_dir = c_root_dir.join(PREGENERATED);
+        if target.os == WINDOWS && target.env == "msvc"
+        {
+            let mut pending = vec![(pregenerated_dir.clone(), out_dir.clone())];
+            while let Some((src_dir, dst_dir)) = pending.pop() {
+                fs::create_dir_all(&dst_dir).unwrap();
+                for entry in fs::read_dir(&src_dir).unwrap() {
+                    let entry = entry.unwrap();
+                    let src_path = entry.path();
+                    let dst_path = dst_dir.join(entry.file_name());
+                    if entry.file_type().unwrap().is_dir() {
+                        pending.push((src_path, dst_path));
+                    } else {
+                        fs::copy(&src_path, &dst_path).unwrap();
+                    }
+                }
+            }
+            out_dir.clone()
+        } else {
+            pregenerated_dir
+        }
     } else {
         generate_sources_and_preassemble(
             &out_dir,
@@ -561,7 +581,13 @@
     let compiler = c.get_compiler();
     // FIXME: On Windows AArch64 we currently must use Clang to compile C code
     let compiler = if target.os == WINDOWS && target.arch == AARCH64 && !compiler.is_like_clang() {
-        let _ = c.compiler("clang");
+        // Keep inherited MSVC flags compatible with the selected Clang driver.
+        let clang = if compiler.is_like_msvc() {
+            "clang-cl"
+        } else {
+            "clang"
+        };
+        let _ = c.compiler(clang);
         c.get_compiler()
     } else {
         compiler
@@ -569,6 +595,15 @@
 
     let _ = c.include(c_root_dir.join("include"));
     let _ = c.include(include_dir);
+    let _ = c.include(c_root_dir.join("third_party").join("fiat"));
+    if compiler.is_like_msvc() {
+        let _ = c.include(c_root_dir.join("crypto").join("curve25519"));
+        let _ = c.include(c_root_dir.join("crypto").join("limbs"));
+        let _ = c.include(c_root_dir.join("crypto").join("fipsmodule").join("aes"));
+        let _ = c.include(c_root_dir.join("crypto").join("fipsmodule").join("bn"));
+        let _ = c.include(c_root_dir.join("crypto").join("fipsmodule").join("ec"));
+        let _ = c.include(c_root_dir.join("crypto").join("poly1305"));
+    }
     for f in cpp_flags(&compiler) {
         let _ = c.flag(f);
     }
diff --git a/crypto/curve25519/curve25519.c b/crypto/curve25519/curve25519.c
index 99d7d7fbb..2f69ad560 100644
--- a/crypto/curve25519/curve25519.c
+++ b/crypto/curve25519/curve25519.c
@@ -47,11 +47,11 @@
 #if defined(__GNUC__)
 #pragma GCC diagnostic ignored "-Wpedantic"
 #endif
-#include "../../third_party/fiat/curve25519_64.h"
+#include "curve25519_64.h"
 #elif defined(OPENSSL_64_BIT)
-#include "../../third_party/fiat/curve25519_64_msvc.h"
+#include "curve25519_64_msvc.h"
 #else
-#include "../../third_party/fiat/curve25519_32.h"
+#include "curve25519_32.h"
 #endif
 
 
diff --git a/crypto/curve25519/curve25519_64_adx.c b/crypto/curve25519/curve25519_64_adx.c
index 88964a9dd..b660f55f4 100644
--- a/crypto/curve25519/curve25519_64_adx.c
+++ b/crypto/curve25519/curve25519_64_adx.c
@@ -19,5 +19,5 @@
 #pragma GCC diagnostic ignored "-Wpedantic"
 #pragma GCC diagnostic ignored "-Wsign-conversion"
 
-#include "../../third_party/fiat/curve25519_64_adx.h"
+#include "curve25519_64_adx.h"
 #endif
diff --git a/crypto/fipsmodule/ec/p256.c b/crypto/fipsmodule/ec/p256.c
index 0117916da..4224d1192 100644
--- a/crypto/fipsmodule/ec/p256.c
+++ b/crypto/fipsmodule/ec/p256.c
@@ -50,11 +50,11 @@
 #if defined(__GNUC__)
 #pragma GCC diagnostic ignored "-Wpedantic"
 #endif
-#include "../../../third_party/fiat/p256_64.h"
+#include "p256_64.h"
 #elif defined(OPENSSL_64_BIT)
-#include "../../../third_party/fiat/p256_64_msvc.h"
+#include "p256_64_msvc.h"
 #else
-#include "../../../third_party/fiat/p256_32.h"
+#include "p256_32.h"
 #endif