diff --git a/fmd5sum/__init__.py b/fmd5sum/__init__.py
index a0b0ce8..0e6e30a 100644
--- a/fmd5sum/__init__.py
+++ b/fmd5sum/__init__.py
@@ -1,6 +1,6 @@
-from .fmd5sum import md5sum, main
+from .fmd5sum import md5sum, main, process_files
 
-__all__ = ["md5sum", "main"]
+__all__ = ["md5sum", "main", "process_files"]
 
 __version__ = "0.2.0"
 __author__ = "Jiale Chen"
diff --git a/fmd5sum/fmd5sum.py b/fmd5sum/fmd5sum.py
index 5d9340e..625b5b0 100644
--- a/fmd5sum/fmd5sum.py
+++ b/fmd5sum/fmd5sum.py
@@ -6,9 +6,13 @@
 
 def md5sum(filename, blocksize=65536):
     """Optimized MD5 checksum calculator with low-level file I/O."""
+    OPEN_FLAGS = os.O_RDONLY
+    if sys.platform.startswith("win32"):
+        OPEN_FLAGS |= os.O_BINARY
+
     hash_md5 = hashlib.md5()
     try:
-        fd = os.open(filename, os.O_RDONLY | os.O_BINARY)
+        fd = os.open(filename, OPEN_FLAGS)
         with open(fd, "rb", closefd=True) as f:
             while True:
                 block = f.read(blocksize)