diff --git a/CMakeLists.txt b/CMakeLists.txt
index add0c1a..bdfaee4 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -8,6 +8,7 @@
 elseif(MSVC)
 	# Disable warnings for implicit integer narrowing.
 	set(CMAKE_C_FLAGS "/wd4267")
+	set(CMAKE_CXX_FLAGS "/wd4267")
 endif()
 
 add_definitions(-DBORINGSSL_IMPLEMENTATION)
diff --git a/tool/CMakeLists.txt b/tool/CMakeLists.txt
index e513c8b..e504838 100644
--- a/tool/CMakeLists.txt
+++ b/tool/CMakeLists.txt
@@ -11,7 +11,7 @@
 	tool.cc
 )
 
-if (APPLE)
+if (APPLE OR WIN32)
 	target_link_libraries(bssl ssl crypto)
 else()
 	target_link_libraries(bssl ssl crypto -lrt)
diff --git a/tool/client.cc b/tool/client.cc
index 6cc93d6..21ea8ba 100644
--- a/tool/client.cc
+++ b/tool/client.cc
@@ -14,6 +14,9 @@
 
 #include <openssl/base.h>
 
+// TODO(davidben): bssl client does not work on Windows.
+#if !defined(OPENSSL_WINDOWS)
+
 #include <string>
 #include <vector>
 
@@ -299,3 +302,5 @@
   SSL_CTX_free(ctx);
   return ok;
 }
+
+#endif  // !OPENSSL_WINDOWS
\ No newline at end of file
diff --git a/tool/pkcs12.cc b/tool/pkcs12.cc
index d35ba0b..fca8bb2 100644
--- a/tool/pkcs12.cc
+++ b/tool/pkcs12.cc
@@ -12,6 +12,8 @@
  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
 
+#include <openssl/base.h>
+
 #include <memory>
 #include <string>
 #include <vector>
@@ -21,7 +23,11 @@
 #include <stdint.h>
 #include <sys/stat.h>
 #include <sys/types.h>
+#if defined(OPENSSL_WINDOWS)
+#include <io.h>
+#else
 #include <unistd.h>
+#endif
 
 #include <openssl/bytestring.h>
 #include <openssl/pem.h>
@@ -31,6 +37,12 @@
 #include "internal.h"
 
 
+#if defined(OPENSSL_WINDOWS)
+typedef int read_result_t;
+#else
+typedef ssize_t read_result_t;
+#endif
+
 static const struct argument kArguments[] = {
     {
      "-dump", false, "Dump the key and contents of the given file to stdout",
@@ -64,7 +76,7 @@
   const size_t size = st.st_size;
 
   std::unique_ptr<uint8_t[]> contents(new uint8_t[size]);
-  ssize_t n;
+  read_result_t n;
   size_t off = 0;
   do {
     n = read(fd, &contents[off], size - off);
diff --git a/tool/tool.cc b/tool/tool.cc
index a0866d7..f35cc7c 100644
--- a/tool/tool.cc
+++ b/tool/tool.cc
@@ -19,7 +19,9 @@
 #include <openssl/ssl.h>
 
 
+#if !defined(OPENSSL_WINDOWS)
 bool Client(const std::vector<std::string> &args);
+#endif
 bool DoPKCS12(const std::vector<std::string> &args);
 bool Speed(const std::vector<std::string> &args);
 
@@ -42,8 +44,10 @@
 
   if (tool == "speed") {
     return !Speed(args);
+#if !defined(OPENSSL_WINDOWS)
   } else if (tool == "s_client" || tool == "client") {
     return !Client(args);
+#endif
   } else if (tool == "pkcs12") {
     return !DoPKCS12(args);
   } else {