diff --git a/.gitignore b/.gitignore
index 674e00875..9abe79ec7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,6 +7,7 @@
 *.clean
 *.ilean
 *.d
+*.lock
 a.out
 build
 GPATH
diff --git a/src/util/file_lock.cpp b/src/util/file_lock.cpp
index e9326a2d5..64655d655 100644
--- a/src/util/file_lock.cpp
+++ b/src/util/file_lock.cpp
@@ -8,17 +8,68 @@ Author: Leonardo de Moura
 #include "util/exception.h"
 #include "util/sstream.h"
 #include "util/file_lock.h"
-#ifdef _WINDOWS
-namespace lean {
-file_lock::file_lock(char const *, bool) {
-    // TODO(Leo):
+#include <sys/file.h>
+
+#ifdef LEAN_WINDOWS
+#include <windows.h>
+#include <io.h>
+#define   LOCK_SH   1    /* shared lock */
+#define   LOCK_EX   2    /* exclusive lock */
+#define   LOCK_NB   4    /* don't block when locking */
+#define   LOCK_UN   8    /* unlock */
+			
+static BOOL lock(HANDLE h, int non_blocking, int exclusive) {
+    DWORD lower, upper;
+    OVERLAPPED ovlp;
+    int flags = 0;
+    
+    lower = GetFileSize(h, &upper);
+    memset (&ovlp, 0, sizeof(ovlp));
+    
+    if (non_blocking)
+	flags |= LOCKFILE_FAIL_IMMEDIATELY;
+    if (exclusive)
+	flags |= LOCKFILE_EXCLUSIVE_LOCK;
+    
+    return LockFileEx(h, flags, 0, lower, upper, &ovlp);
 }
-file_lock::~file_lock() {
+
+static BOOL unlock(HANDLE h) {
+    DWORD lower, upper;
+    lower = GetFileSize(h, &upper);
+    return UnlockFile(h, 0, 0, lower, upper);
 }
+
+int flock(int fd, int op) {
+    HANDLE h = (HANDLE)_get_osfhandle(fd);
+    DWORD res;
+    int non_blocking;
+    
+    if (h == INVALID_HANDLE_VALUE)
+	return -1;
+    
+    non_blocking = op & LOCK_NB;
+    op          &= ~LOCK_NB;
+    
+    switch (op) {
+    case LOCK_SH:
+	res = lock(h, non_blocking, 0);
+	break;
+    case LOCK_EX:
+	res = lock(h, non_blocking, 1);
+	break;
+    case LOCK_UN:
+	res = unlock(h);
+	break;
+    default:
+	return -1;
+    }
+    return !res ? -1 : 0;
 }
 #else
 #include <unistd.h>
-#include <sys/file.h>
+#endif
+
 namespace lean {
 file_lock::file_lock(char const * fname, bool exclusive):
     m_fname(fname), m_fd(-1) {
@@ -39,4 +90,3 @@ file_lock::~file_lock() {
     }
 }
 }
-#endif