diff --git a/include-hax/fake_masm/macamd64.inc b/include-hax/fake_masm/macamd64.inc
new file mode 100644
index 0000000000..970487f4dc
--- /dev/null
+++ b/include-hax/fake_masm/macamd64.inc
@@ -0,0 +1,9 @@
+push_reg macro Reg
+	push Reg
+	.pushreg Reg
+	endm
+
+alloc_stack macro Size
+	sub rsp, Size
+	.allocstack Size
+	endm
diff --git a/src/include/nacl_compiler_annotations.h b/src/include/nacl_compiler_annotations.h
index c9baad67b7..b8e46d2f26 100644
--- a/src/include/nacl_compiler_annotations.h
+++ b/src/include/nacl_compiler_annotations.h
@@ -10,7 +10,7 @@
 #include "native_client/src/include/build_config.h"
 
 /* MSVC supports "inline" only in C++ */
-#if NACL_WINDOWS
+#if defined(_MSC_VER)
 # define INLINE __forceinline
 #else
 # define INLINE __inline__
diff --git a/src/include/portability.h b/src/include/portability.h
index d0360ebfa9..42aab4d5a5 100644
--- a/src/include/portability.h
+++ b/src/include/portability.h
@@ -16,6 +16,7 @@
 #ifndef NATIVE_CLIENT_SRC_INCLUDE_PORTABILITY_H_
 #define NATIVE_CLIENT_SRC_INCLUDE_PORTABILITY_H_ 1
 
+#include <stdint.h>
 #include <stdlib.h>
 
 #include "native_client/src/include/build_config.h"
@@ -30,7 +31,9 @@
 
 #if NACL_WINDOWS
 /* disable warnings for deprecated functions like getenv, etc. */
+#if defined(_MSC_VER)
 #pragma warning(disable : 4996)
+#endif
 # include <malloc.h>
 /* TODO: eliminate port_win.h */
 # include "native_client/src/include/win/port_win.h"
@@ -59,7 +62,7 @@
 #define GG_UINT32_C(x)  (x ## U)
 #define GG_UINT64_C(x)  GG_ULONGLONG(x)
 
-#if NACL_WINDOWS
+#if NACL_WINDOWS && defined(_MSC_VER)
 #define GG_LONGLONG(x) x##I64
 #define GG_ULONGLONG(x) x##UI64
 #else
diff --git a/src/include/portability_io.h b/src/include/portability_io.h
index 75eedbf12d..8abafd023f 100644
--- a/src/include/portability_io.h
+++ b/src/include/portability_io.h
@@ -17,7 +17,9 @@
 
 #if NACL_WINDOWS
 /* disable warnings for deprecated _snprintf */
+#if defined(_MSC_VER)
 #pragma warning(disable : 4996)
+#endif
 
 #include <io.h>
 #include <direct.h>
@@ -43,7 +45,9 @@
 /* missing from win stdio.h and fcntl.h */
 
 /* from bits/fcntl.h */
+#if defined(_MSC_VER)
 #define O_ACCMODE 0003
+#endif
 
 #else
 
diff --git a/src/include/portability_string.h b/src/include/portability_string.h
index 9b86ead994..1c49954770 100644
--- a/src/include/portability_string.h
+++ b/src/include/portability_string.h
@@ -53,7 +53,9 @@ size_t strnlen(const char* str, size_t max);
 
 #if NACL_WINDOWS
 /* disable warnings for deprecated strncpy */
+#if defined(_MSC_VER)
 #pragma warning(disable : 4996)
+#endif
 
 #define STRDUP _strdup
 #define STRTOLL _strtoi64
diff --git a/src/include/win/port_win.h b/src/include/win/port_win.h
index 790a8fe3e8..8130db69c2 100644
--- a/src/include/win/port_win.h
+++ b/src/include/win/port_win.h
@@ -38,6 +38,7 @@
 
 /* TODO: eliminated this file and move its contents to portability*.h */
 
+#if defined(_MSC_VER)
 /* wchar_t and unsigned short are not always equivalent*/
 #pragma warning(disable : 4255)
 /* padding added after struct member */
@@ -46,6 +47,7 @@
 #pragma warning(disable: 4826)
 /* conditional expression is constant */
 #pragma warning(disable : 4127)
+#endif
 
 /* TODO: limit this include to files that really need it */
 #ifndef NOMINMAX
@@ -74,7 +76,9 @@ typedef __int64_t         int64_t;
 typedef __uint64_t        uint64_t;
 
 typedef long              off_t;
+#if defined(_MSC_VER)
 typedef int               mode_t;
+#endif
 typedef long              _off_t;
 typedef long int          __loff_t;
 typedef unsigned long     DWORD;
@@ -94,7 +98,7 @@ typedef int32_t           ssize_t;
  *
  * Only including range values actually used in our codebase.
  */
-#if _MSC_VER >= 1800
+#if !defined(_MSC_VER) || _MSC_VER >= 1800
 #include <stdint.h>
 #else
 # if !defined(UINT8_MAX)
@@ -160,6 +164,8 @@ EXTERN_C_END
 
 
 /* from linux/limits.h, via sys/param.h */
+#if defined(_MSC_VER)
 #define PATH_MAX 4096
+#endif
 
 #endif  /* NATIVE_CLIENT_SRC_INCLUDE_WIN_PORT_WIN_H_ */
diff --git a/src/shared/platform/win/lock_impl.h b/src/shared/platform/win/lock_impl.h
index cb5f98b8d3..9024ea3a06 100644
--- a/src/shared/platform/win/lock_impl.h
+++ b/src/shared/platform/win/lock_impl.h
@@ -8,7 +8,7 @@
 #ifndef NATIVE_CLIENT_SRC_TRUSTED_PLATFORM_WIN_LOCK_IMPL_H_
 #define NATIVE_CLIENT_SRC_TRUSTED_PLATFORM_WIN_LOCK_IMPL_H_
 
-#include <Windows.h>
+#include <windows.h>
 #include "native_client/src/include/nacl_macros.h"
 #include "native_client/src/shared/platform/nacl_sync.h"
 
diff --git a/src/shared/platform/win/nacl_exit.c b/src/shared/platform/win/nacl_exit.c
index a190175ff5..17c7741d89 100644
--- a/src/shared/platform/win/nacl_exit.c
+++ b/src/shared/platform/win/nacl_exit.c
@@ -39,7 +39,11 @@ void NaClAbort(void) {
    * http://code.google.com/p/nativeclient/issues/detail?id=2772).
    */
   while (1) {
+#if defined(_MSC_VER)
     __halt();
+#else
+    __asm__("hlt");
+#endif
   }
 }
 
diff --git a/src/shared/platform/win/port_win.c b/src/shared/platform/win/port_win.c
index 2f303ff10a..d743bd1c49 100644
--- a/src/shared/platform/win/port_win.c
+++ b/src/shared/platform/win/port_win.c
@@ -12,7 +12,7 @@
 
 #include "native_client/src/include/portability.h"
 
-#if ( DO_NOT_USE_FAST_ASSEMBLER_VERSION_FOR_FFS || defined(_WIN64) )
+#if ( DO_NOT_USE_FAST_ASSEMBLER_VERSION_FOR_FFS || defined(_WIN64) || !defined(_MSC_VER) )
 int ffs(int x) {
   int r = 1;
 
diff --git a/src/shared/platform/win/xlate_system_error.c b/src/shared/platform/win/xlate_system_error.c
index cfaca7c266..b9d51f34fd 100644
--- a/src/shared/platform/win/xlate_system_error.c
+++ b/src/shared/platform/win/xlate_system_error.c
@@ -9,7 +9,7 @@
  */
 
 #include <errno.h>
-#include <WinError.h>
+#include <winerror.h>
 
 #include "native_client/src/shared/platform/nacl_log.h"
 #include "native_client/src/shared/platform/win/xlate_system_error.h"
diff --git a/src/trusted/fault_injection/fault_injection.c b/src/trusted/fault_injection/fault_injection.c
index 3d71f5f7b2..2fa29c35d9 100644
--- a/src/trusted/fault_injection/fault_injection.c
+++ b/src/trusted/fault_injection/fault_injection.c
@@ -66,6 +66,8 @@
  */
 # define NACL_HAS_STRNDUP   0
 /* could use TLS if not built into a DLL, otherwise must use TLSALLOC */
+# define NACL_USE_TLS       0
+# define NACL_USE_TSD       0
 # define NACL_USE_TLSALLOC  1
 # include <windows.h>
 #endif
diff --git a/src/trusted/platform_qualify/arch/x86/vcpuid.c b/src/trusted/platform_qualify/arch/x86/vcpuid.c
index dbefa9b11c..a5ec005d4b 100644
--- a/src/trusted/platform_qualify/arch/x86/vcpuid.c
+++ b/src/trusted/platform_qualify/arch/x86/vcpuid.c
@@ -38,7 +38,15 @@ const int kMagicConst_ROUNDSS = 0xc0000000;
 const int kMagicConst_POPCNT = 13;
 const int kMagicConst_CRC32  = 0xb906c3ea;
 
-#if !(NACL_WINDOWS && (NACL_BUILD_SUBARCH == 64))
+#if (NACL_WINDOWS && defined(_MSC_VER) && (NACL_BUILD_SUBARCH == 64))
+# define NACL_WINDOWS_MSC_64
+#endif
+
+#if (NACL_WINDOWS && !defined(_MSC_VER))
+# define NACL_WINDOWS_MINGW
+#endif
+
+#if !defined(NACL_WINDOWS_MSC_64)
 static int asm_HasMMX(void) {
   volatile int before, after;
   before = kMagicConst;
@@ -386,20 +394,34 @@ static int asm_HasCX8(void) {
 #endif  /* 0 */
 #endif  /* 64-bit Windows */
 
-#if NACL_WINDOWS && (NACL_BUILD_SUBARCH == 64)
+#if defined(NACL_WINDOWS_MSC_64)
 static int CheckCPUFeatureDetection(NaClCPUFeaturesX86 *cpuf) {
   /* Unfortunately the asm_ tests will not work on 64-bit Windows */
   return 0;
 }
 #else
-#if (NACL_LINUX || NACL_OSX)
+#if (NACL_LINUX || NACL_OSX || defined(NACL_WINDOWS_MINGW))
 /* Linux/MacOS signal handling code, for trapping illegal instruction faults */
 static int sawbadinstruction = 0;
-static struct sigaction crash_detect;
 static int signum;
 
-sigjmp_buf crash_load;
+#if defined(NACL_WINDOWS_MINGW)
+static PVOID crash_handler;
+static jmp_buf crash_load;
+#else
+static struct sigaction crash_detect;
+static sigjmp_buf crash_load;
+#endif
 
+#if defined(NACL_WINDOWS_MINGW)
+static LONG CALLBACK handler_load(EXCEPTION_POINTERS *ep)
+{
+  if (ep->ExceptionRecord->ExceptionCode == EXCEPTION_ILLEGAL_INSTRUCTION) {
+      longjmp(crash_load, SIGILL);
+  }
+  return EXCEPTION_CONTINUE_SEARCH;
+}
+#else
 void  handler_load(int  signal_num) {
   siglongjmp(crash_load, signal_num);
 }
@@ -427,13 +449,18 @@ void  all_sigs(struct sigaction *new_action,
   (void) sigaction(SIGCHLD, &ign, 0);
   (void) sigaction(SIGTSTP, &ign, 0);
 }
+#endif
 
 static void SignalInit(void) {
   sawbadinstruction = 0;
+#if defined(NACL_WINDOWS_MINGW)
+  crash_handler = AddVectoredExceptionHandler(1, handler_load);
+#else
   crash_detect.sa_handler = handler_load;
   sigemptyset(&crash_detect.sa_mask);
   crash_detect.sa_flags = SA_RESETHAND;
   all_sigs(&crash_detect, 0);
+#endif
 }
 
 static void SetSawBadInst(void) {
@@ -450,7 +477,13 @@ static int SawBadInst(void) {
  */
 static int DoTest(int (*thetest)(void), const char *s) {
   SignalInit();
-  if (0 != (signum = sigsetjmp(crash_load, 1))) {
+
+#if defined(NACL_WINDOWS_MINGW)
+  signum = setjmp(crash_load);
+#else
+  signum = sigsetjmp(crash_load, 1);
+#endif
+  if (0 != signum) {
     SetSawBadInst();
     if (SIGILL == signum) {
       fprintf(stderr, "%s: illegal instruction\n", s);
@@ -462,10 +495,16 @@ static int DoTest(int (*thetest)(void), const char *s) {
     int hasfeature = thetest();
     if (hasfeature && (! SawBadInst())) {
       printf("[Has %s]\n", s);
+#if defined(NACL_WINDOWS_MINGW)
+      RemoveVectoredExceptionHandler(crash_handler);
+#endif
       return 0;
     }
   }
   printf("no %s\n", s);
+#if defined(NACL_WINDOWS_MINGW)
+  RemoveVectoredExceptionHandler(crash_handler);
+#endif
   return 1;
 }
 #elif NACL_WINDOWS
diff --git a/src/trusted/service_runtime/arch/x86_32/sel_rt_32.c b/src/trusted/service_runtime/arch/x86_32/sel_rt_32.c
index 5757b6c904..15d543639e 100644
--- a/src/trusted/service_runtime/arch/x86_32/sel_rt_32.c
+++ b/src/trusted/service_runtime/arch/x86_32/sel_rt_32.c
@@ -90,7 +90,7 @@ int NaClAppThreadInitArchSpecific(struct NaClAppThread *natp,
    * Save the system's state of the x87 FPU control word so we can restore
    * the same state when returning to trusted code.
    */
-#if NACL_WINDOWS
+#if defined(_MSC_VER)
   {
     uint16_t sys_fcw;
     __asm {
diff --git a/src/trusted/service_runtime/arch/x86_64/nacl_switch_unwind_win.asm b/src/trusted/service_runtime/arch/x86_64/nacl_switch_unwind_win.asm
index d5dd93a9a1..6ead09486a 100644
--- a/src/trusted/service_runtime/arch/x86_64/nacl_switch_unwind_win.asm
+++ b/src/trusted/service_runtime/arch/x86_64/nacl_switch_unwind_win.asm
@@ -2,7 +2,7 @@
 ; Use of this source code is governed by a BSD-style license that can be
 ; found in the LICENSE file.
 
-include ksamd64.inc
+include macamd64.inc
 
 EXTERN NaClSwitch : QWORD
 
diff --git a/src/trusted/service_runtime/nacl_signal.h b/src/trusted/service_runtime/nacl_signal.h
index e3a8fa1732..2301ed407e 100644
--- a/src/trusted/service_runtime/nacl_signal.h
+++ b/src/trusted/service_runtime/nacl_signal.h
@@ -58,7 +58,7 @@ struct NaClExceptionFrame;
 #define NACL_ABI_WIFSIGNALED(status) ((((status) + 1) & 0x7f) > 1)
 #define NACL_ABI_W_EXITCODE(ret, sig) ((((ret) & 0xff) << 8) + ((sig) & 0x7f))
 
-#if NACL_WINDOWS
+#if NACL_WINDOWS && defined(_MSC_VER)
 enum PosixSignals {
   SIGINT  = 2,
   SIGQUIT = 3,
diff --git a/src/trusted/service_runtime/sel_ldr.c b/src/trusted/service_runtime/sel_ldr.c
index 4dbc7611cb..7bcf97c210 100644
--- a/src/trusted/service_runtime/sel_ldr.c
+++ b/src/trusted/service_runtime/sel_ldr.c
@@ -912,7 +912,7 @@ void NaClVmIoPendingCheck_mu(struct NaClApp *nap,
  * We need its symbol in the symbol table so don't inline it.
  * TODO(dje): add some explanation for the non-GDB person.
  */
-#if NACL_WINDOWS
+#if NACL_WINDOWS && defined(_MSVC_VER)
 __declspec(dllexport noinline)
 #endif
 #ifdef __GNUC__
diff --git a/src/trusted/validator/validation_cache.c b/src/trusted/validator/validation_cache.c
index b9d9536bb7..f8ce53e9ef 100644
--- a/src/trusted/validator/validation_cache.c
+++ b/src/trusted/validator/validation_cache.c
@@ -21,7 +21,7 @@
 #include "native_client/src/trusted/validator/validation_metadata.h"
 
 #if NACL_WINDOWS
-#include <Windows.h>
+#include <windows.h>
 #include <io.h>
 #endif
 
diff --git a/src/trusted/validator_ragel/bitmap.h b/src/trusted/validator_ragel/bitmap.h
index dec2a0d2cb..798e392b72 100644
--- a/src/trusted/validator_ragel/bitmap.h
+++ b/src/trusted/validator_ragel/bitmap.h
@@ -15,7 +15,7 @@
 #include "native_client/src/include/nacl_macros.h"
 #include "native_client/src/include/portability.h"
 
-#if NACL_WINDOWS
+#if defined(_MSC_VER)
 # define FORCEINLINE __forceinline
 #else
 # define FORCEINLINE __inline __attribute__ ((always_inline))
diff --git a/src/trusted/validator_ragel/decoding.h b/src/trusted/validator_ragel/decoding.h
index 64087b7621..51a781d14e 100644
--- a/src/trusted/validator_ragel/decoding.h
+++ b/src/trusted/validator_ragel/decoding.h
@@ -19,7 +19,7 @@
 #include "native_client/src/include/build_config.h"
 #include "native_client/src/trusted/validator_ragel/decoder.h"
 
-#if NACL_WINDOWS
+#if defined(_MSC_VER)
 # define FORCEINLINE __forceinline
 #else
 # define FORCEINLINE __inline __attribute__ ((always_inline))