diff --git a/Lib/pathlib.py b/Lib/pathlib.py
index d42ee4dc90..aa9a731785 100644
--- a/Lib/pathlib.py
+++ b/Lib/pathlib.py
@@ -1129,24 +1129,26 @@ def read_text(self, encoding=None, errors=None):
         with self.open(mode='r', encoding=encoding, errors=errors) as f:
             return f.read()
 
-    def write_bytes(self, data):
+    def write_bytes(self, data, append=False):
         """
         Open the file in bytes mode, write to it, and close the file.
         """
         # type-check for the buffer interface before truncating the file
         view = memoryview(data)
-        with self.open(mode='wb') as f:
+        mode = 'ab' if append else 'wb'
+        with self.open(mode=mode) as f:
             return f.write(view)
 
-    def write_text(self, data, encoding=None, errors=None, newline=None):
+    def write_text(self, data, encoding=None, errors=None, newline=None, append=False):
         """
         Open the file in text mode, write to it, and close the file.
         """
         if not isinstance(data, str):
             raise TypeError('data must be str, not %s' %
                             data.__class__.__name__)
+        mode = 'at' if append else 'wt'
         encoding = io.text_encoding(encoding)
-        with self.open(mode='w', encoding=encoding, errors=errors, newline=newline) as f:
+        with self.open(mode=mode, encoding=encoding, errors=errors, newline=newline) as f:
             return f.write(data)
 
     def readlink(self):