diff --git a/tftpy/CPFilelock.py b/tftpy/CPFilelock.py
new file mode 100644
index 0000000..a4fafb0
--- /dev/null
+++ b/tftpy/CPFilelock.py
@@ -0,0 +1,69 @@
+import os
+import platform
+import time
+import errno
+
+class FileLock:
+    """ A cross-platform file lock solution. """
+
+    def __init__(self, file_obj):
+        self.file_obj = file_obj
+        self.fd = file_obj.fileno()
+        self.is_windows = platform.system() == 'Windows'
+        
+    def acquire_shared(self):
+        if self.is_windows:
+            self._win32_lock(shared=True)
+        else:
+            self._posix_lock(shared=True)
+            
+
+    def acquire_exclusive(self):
+        if self.is_windows:
+            self._win32_lock(shared=False)
+        else:
+            self._posix_lock(shared=False)
+            
+
+    def release(self):
+        if self.is_windows:
+            self._win32_unlock()
+        else:
+            self._posix_unlock()
+            
+    def _win32_lock(self, shared=True):
+        lockfile = f"{self.file_obj.name}.lock"
+        while True:
+            try:
+                fd = os.open(lockfile, 
+                           os.O_CREAT | os.O_EXCL | os.O_RDWR)
+                os.close(fd)
+                break
+            except OSError as e:
+                if e.errno != errno.EEXIST:
+                    raise
+                time.sleep(0.1)
+                
+
+    def _win32_unlock(self):
+        try:
+            os.unlink(f"{self.file_obj.name}.lock")
+        except OSError:
+            pass
+            
+            
+    def _posix_lock(self, shared=True):
+        import fcntl
+        flags = fcntl.LOCK_SH if shared else fcntl.LOCK_EX
+        try:
+            fcntl.flock(self.fd, flags | fcntl.LOCK_NB)
+        except IOError as e:
+            raise OSError(f"Failed to acquire lock: {e}")
+    
+            
+    def _posix_unlock(self):
+        import fcntl
+        try:
+            fcntl.flock(self.fd, fcntl.LOCK_UN)
+        except IOError as e:
+            raise OSError(f"Failed to release lock: {e}")
\ No newline at end of file
diff --git a/tftpy/TftpContexts.py b/tftpy/TftpContexts.py
index 831b117..014465e 100644
--- a/tftpy/TftpContexts.py
+++ b/tftpy/TftpContexts.py
@@ -15,6 +15,7 @@
 import socket
 import sys
 import time
+from .CPFilelock import FileLock
 
 from .TftpPacketFactory import TftpPacketFactory
 from .TftpPacketTypes import *
@@ -134,7 +135,7 @@ def __del__(self):
     def __enter__(self):
         log.debug("__enter__ on TftpContext")
         return self
-
+        
     def __exit__(self, type, value, traceback):
         log.debug("__exit__ on TftpContext")
         self.end()
@@ -165,7 +166,8 @@ def end(self, close_fileobj=True):
         if close_fileobj and self.fileobj is not None and not self.fileobj.closed:
             log.debug("self.fileobj is open - closing")
             if self.flock:
-                lockfile(self.fileobj, unlock=True)
+                if self.flock and hasattr(self, "filelock"):
+                    self.filelock.release()
             self.fileobj.close()
 
     def gethost(self):
@@ -335,7 +337,12 @@ def __init__(
             if self.flock:
                 log.debug("locking input file %s", input)
                 try:
-                    lockfile(self.fileobj, shared=True, blocking=False)
+                    self.filelock = FileLock(self.fileobj)
+                    try:
+                        self.filelock.acquire_shared()
+                    except OSError as err:
+                        log.error("Failed to acquire read lock on file %s", input)
+                        raise
                 except OSError as err:
                     log.error("Failed to acquire read lock on file %s", input)
                     raise
@@ -346,7 +353,7 @@ def __init__(
     def __del__(self):
         log.debug("TftpContextClientUpload.__del__")
         super().__del__()
-
+        
     def __str__(self):
         return f"{self.host}:{self.port} {self.state}"
 
@@ -431,7 +438,12 @@ def __init__(
             if self.flock:
                 log.debug("locking file for writing: %s", output)
                 try:
-                    lockfile(self.fileobj, shared=False, blocking=False)
+                    self.filelock = FileLock(self.fileobj)
+                    try:
+                        self.filelock.acquire_exclusive()
+                    except OSError as err:
+                        log.error("Failed to acquire write lock on output file %s: %s", output, err)
+                        raise
                 except OSError as err:
                     log.error("Failed to acquire write lock on output file %s: %s", output, err)
                     raise