diff --git a/borg/helpers.py b/borg/helpers.py
index b38ec9455..7c4a0fa91 100644
--- a/borg/helpers.py
+++ b/borg/helpers.py
@@ -55,9 +55,15 @@ class Error(Exception):
     # show a traceback?
     traceback = False
 
+    def __init__(self, *args):
+        super().__init__(*args)
+        self.args = args
+
     def get_message(self):
         return type(self).__doc__.format(*self.args)
 
+    __str__ = get_message
+
 
 class ErrorWithTraceback(Error):
     """like Error, but show a traceback also"""
@@ -699,6 +705,10 @@ class Buffer:
     """
     provide a thread-local buffer
     """
+
+    class MemoryLimitExceeded(Error, OSError):
+        """Requested buffer size {} is above the limit of {}."""
+
     def __init__(self, allocator, size=4096, limit=None):
         """
         Initialize the buffer: use allocator(size) call to allocate a buffer.
@@ -718,11 +728,11 @@ class Buffer:
         """
         resize the buffer - to avoid frequent reallocation, we usually always grow (if needed).
         giving init=True it is possible to first-time initialize or shrink the buffer.
-        if a buffer size beyond the limit is requested, raise ValueError.
+        if a buffer size beyond the limit is requested, raise Buffer.MemoryLimitExceeded (OSError).
         """
         size = int(size)
         if self.limit is not None and size > self.limit:
-            raise ValueError('Requested buffer size %d is above the limit of %d.' % (size, self.limit))
+            raise Buffer.MemoryLimitExceeded(size, self.limit)
         if init or len(self) < size:
             self._thread_local.buffer = self.allocator(size)
 
diff --git a/borg/testsuite/helpers.py b/borg/testsuite/helpers.py
index 47d49f999..3f9c70969 100644
--- a/borg/testsuite/helpers.py
+++ b/borg/testsuite/helpers.py
@@ -793,7 +793,7 @@ class TestBuffer:
         buffer = Buffer(bytearray, size=100, limit=200)
         buffer.resize(200)
         assert len(buffer) == 200
-        with pytest.raises(ValueError):
+        with pytest.raises(Buffer.MemoryLimitExceeded):
             buffer.resize(201)
         assert len(buffer) == 200
 
@@ -807,7 +807,7 @@ class TestBuffer:
         b3 = buffer.get(200)
         assert len(b3) == 200
         assert b3 is not b2  # new, resized buffer
-        with pytest.raises(ValueError):
+        with pytest.raises(Buffer.MemoryLimitExceeded):
             buffer.get(201)  # beyond limit
         assert len(buffer) == 200
 
diff --git a/borg/xattr.py b/borg/xattr.py
index 0c1e9f0eb..75cb91890 100644
--- a/borg/xattr.py
+++ b/borg/xattr.py
@@ -10,7 +10,7 @@ from ctypes import CDLL, create_string_buffer, c_ssize_t, c_size_t, c_char_p, c_
 from ctypes.util import find_library
 from distutils.version import LooseVersion
 
-from .helpers import Buffer, Error
+from .helpers import Buffer
 
 
 try:
@@ -113,11 +113,8 @@ def split_lstring(buf):
     return result
 
 
-class BufferTooSmallError(OSError):
-    """insufficient buffer memory for completing a xattr operation."""
-
-    def __str__(self):
-        return self.__doc__
+class BufferTooSmallError(Exception):
+    """the buffer given to an xattr function was too small for the result."""
 
 
 def _check(rv, path=None, detect_buffer_too_small=False):