Index: lib/profile/GCDAProfiling.c
===================================================================
--- lib/profile/GCDAProfiling.c
+++ lib/profile/GCDAProfiling.c
@@ -29,6 +29,8 @@
 #include <string.h>
 
 #if defined(_WIN32)
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
 #include "WindowsMMap.h"
 #else
 #include <sys/mman.h>
@@ -58,6 +60,14 @@
 typedef unsigned long long uint64_t;
 #endif
 
+#ifdef __USE_FILE_OFFSET64
+# define DWORD_HI(x) (x >> 32)
+# define DWORD_LO(x) ((x) & 0xffffffff)
+#else
+# define DWORD_HI(x) (0)
+# define DWORD_LO(x) (x)
+#endif
+
 #include "InstrProfiling.h"
 #include "InstrProfilingUtil.h"
 
@@ -86,6 +96,9 @@
 static uint64_t cur_pos = 0;
 static uint64_t file_size = 0;
 static int new_file = 0;
+#if defined(_WIN32)
+static HANDLE mmap_handle = INVALID_HANDLE_VALUE;
+#endif
 static int fd = -1;
 
 typedef void (*fn_ptr)();
@@ -255,6 +268,28 @@
   if (file_size == 0)
     return -1;
 
+#if defined(_WIN32)
+  HANDLE mmap_fd;
+  if (fd == -1)
+    mmap_fd = INVALID_HANDLE_VALUE;
+  else
+    mmap_fd = (HANDLE)_get_osfhandle(fd);
+
+  mmap_handle = CreateFileMapping(mmap_fd, NULL, PAGE_READWRITE, DWORD_HI(file_size), DWORD_LO(file_size), NULL);
+  if (mmap_handle == INVALID_HANDLE_VALUE) {
+    fprintf(stderr, "profiling: %s: cannot create file mapping: %d\n", filename,
+            GetLastError());
+    return -1;
+  }
+
+  write_buffer = MapViewOfFile(mmap_handle, FILE_MAP_WRITE, 0, 0, file_size);
+  if (write_buffer == NULL) {
+    fprintf(stderr, "profiling: %s: cannot map: %d\n", filename,
+            GetLastError());
+    CloseHandle(mmap_handle);
+    return -1;
+  }
+#else
   write_buffer = mmap(0, file_size, PROT_READ | PROT_WRITE,
                       MAP_FILE | MAP_SHARED, fd, 0);
   if (write_buffer == (void *)-1) {
@@ -263,10 +298,18 @@
             strerror(errnum));
     return -1;
   }
+#endif
+
   return 0;
 }
 
 static void unmap_file() {
+#if defined(_WIN32)
+  UnmapViewOfFile(write_buffer);
+  CloseHandle(mmap_handle);
+
+  mmap_handle = INVALID_HANDLE_VALUE;
+#else
   if (msync(write_buffer, file_size, MS_SYNC) == -1) {
     int errnum = errno;
     fprintf(stderr, "profiling: %s: cannot msync: %s\n", filename,
@@ -277,6 +320,8 @@
    * is written and we don't care.
    */
   (void)munmap(write_buffer, file_size);
+#endif
+
   write_buffer = NULL;
   file_size = 0;
 }
Index: test/profile/Inputs/instrprof-gcov-__gcov_flush-multiple.c
===================================================================
--- test/profile/Inputs/instrprof-gcov-__gcov_flush-multiple.c
+++ test/profile/Inputs/instrprof-gcov-__gcov_flush-multiple.c
@@ -0,0 +1,16 @@
+int main(void) {
+  __gcov_flush();
+
+  if (remove("instrprof-gcov-__gcov_flush-multiple.gcda") != 0) {
+    return 1;
+  }
+
+  __gcov_flush();
+  __gcov_flush();
+
+  if (remove("instrprof-gcov-__gcov_flush-multiple.gcda") != 0) {
+    return 1;
+  }
+
+  return 0;
+}
Index: test/profile/Inputs/instrprof-gcov-__gcov_flush-multiple.c.gcov
===================================================================
--- test/profile/Inputs/instrprof-gcov-__gcov_flush-multiple.c.gcov
+++ test/profile/Inputs/instrprof-gcov-__gcov_flush-multiple.c.gcov
@@ -0,0 +1,21 @@
+// CHECK:        -:    0:Source:{{.*}}Inputs/instrprof-gcov-__gcov_flush-multiple.c
+// CHECK-NEXT:        -:    0:Graph:instrprof-gcov-__gcov_flush-multiple.gcno
+// CHECK-NEXT:        -:    0:Data:instrprof-gcov-__gcov_flush-multiple.gcda
+// CHECK-NEXT:        -:    0:Runs:1
+// CHECK-NEXT:        -:    0:Programs:1
+// CHECK-NEXT:    #####:    1:int main(void) {
+// CHECK-NEXT:    #####:    2:  __gcov_flush();
+// CHECK-NEXT:        -:    3:
+// CHECK-NEXT:    #####:    4:  if (remove("instrprof-gcov-__gcov_flush-multiple.gcda") != 0) {
+// CHECK-NEXT:    #####:    5:    return 1;
+// CHECK-NEXT:        -:    6:  }
+// CHECK-NEXT:        -:    7:
+// CHECK-NEXT:    #####:    8:  __gcov_flush();
+// CHECK-NEXT:    #####:    9:  __gcov_flush();
+// CHECK-NEXT:        -:   10:
+// CHECK-NEXT:    #####:   11:  if (remove("instrprof-gcov-__gcov_flush-multiple.gcda") != 0) {
+// CHECK-NEXT:    #####:   12:    return 1;
+// CHECK-NEXT:        -:   13:  }
+// CHECK-NEXT:        -:   14:
+// CHECK-NEXT:        1:   15:  return 0;
+// CHECK-NEXT:        1:   16:}
Index: test/profile/instrprof-gcov-__gcov_flush-multiple.test
===================================================================
--- test/profile/instrprof-gcov-__gcov_flush-multiple.test
+++ test/profile/instrprof-gcov-__gcov_flush-multiple.test
@@ -0,0 +1,10 @@
+RUN: mkdir -p %t.d
+RUN: cd %t.d
+
+RUN: %clang --coverage -o %t %S/Inputs/instrprof-gcov-__gcov_flush-multiple.c
+RUN: test -f instrprof-gcov-__gcov_flush-multiple.gcno
+
+RUN: rm -f instrprof-gcov-__gcov_flush-multiple.gcda
+RUN: %run %t
+RUN: llvm-cov gcov instrprof-gcov-__gcov_flush-multiple.gcda
+RUN: FileCheck --match-full-lines --strict-whitespace --input-file instrprof-gcov-__gcov_flush-multiple.c.gcov %S/Inputs/instrprof-gcov-__gcov_flush-multiple.c.gcov