diff --git a/util/file.h b/util/file.h
index 7a47be95a8d..38eef8ab3b3 100644
--- a/util/file.h
+++ b/util/file.h
@@ -72,7 +72,7 @@ public:
     void open(const char *filename, bool readOnly=false ) {
         fd = CreateFile(
                  toNativeString(filename).c_str(),
-                 ( readOnly ? 0 : GENERIC_WRITE ) | GENERIC_READ, FILE_SHARE_READ,
+                 ( readOnly ? 0 : GENERIC_WRITE ) | GENERIC_READ, FILE_SHARE_WRITE|FILE_SHARE_READ,
                  NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
         if( !is_open() ) {
              DWORD e = GetLastError();
diff --git a/util/mmap_win.cpp b/util/mmap_win.cpp
index e69b50b3582..d7b17fc78a9 100644
--- a/util/mmap_win.cpp
+++ b/util/mmap_win.cpp
@@ -113,7 +113,7 @@ namespace mongo {
             fd = CreateFile(
                      toNativeString(filename).c_str(),
                      rw, // desired access
-                     FILE_SHARE_READ, // share mode
+                     FILE_SHARE_WRITE | FILE_SHARE_READ, // share mode
                      NULL, // security
                      OPEN_ALWAYS, // create disposition
                      createOptions , // flags