diff --git a/tests/test_sync.py b/tests/test_sync.py
index 73937ff..d5779a9 100644
--- a/tests/test_sync.py
+++ b/tests/test_sync.py
@@ -9,6 +9,7 @@
 
 import pytest
 
+import vdirsyncer.exceptions as exceptions
 from vdirsyncer.storage.base import Item
 from vdirsyncer.storage.memory import MemoryStorage
 from vdirsyncer.sync import BothReadOnly, StorageEmpty, SyncConflict, sync
@@ -251,10 +252,14 @@ def test_both_readonly():
 
 def test_readonly():
     a = MemoryStorage()
-    b = MemoryStorage(read_only=True)
+    b = MemoryStorage()
     status = {}
     href_a, _ = a.upload(Item(u'UID:1'))
     href_b, _ = b.upload(Item(u'UID:2'))
+    b.read_only = True
+    with pytest.raises(exceptions.ReadOnlyError):
+        b.upload(Item(u'UID:3'))
+
     sync(a, b, status)
     assert len(status) == 2 and a.has(href_a) and not b.has(href_a)
     sync(a, b, status)
diff --git a/vdirsyncer/exceptions.py b/vdirsyncer/exceptions.py
index e7fd14d..a77e77d 100644
--- a/vdirsyncer/exceptions.py
+++ b/vdirsyncer/exceptions.py
@@ -44,3 +44,7 @@ class AlreadyExistingError(PreconditionFailed):
 
 class WrongEtagError(PreconditionFailed):
     '''Wrong etag'''
+
+
+class ReadOnlyError(Error):
+    '''Storage is read-only.'''
diff --git a/vdirsyncer/storage/base.py b/vdirsyncer/storage/base.py
index 48b0beb..0a3fd64 100644
--- a/vdirsyncer/storage/base.py
+++ b/vdirsyncer/storage/base.py
@@ -7,13 +7,31 @@
     :license: MIT, see LICENSE for more details.
 '''
 
+import functools
 
 from .. import exceptions
 from ..utils import uniq
+from ..utils.compat import with_metaclass
 from ..utils.vobject import Item  # noqa
 
 
-class Storage(object):
+def mutating_storage_method(f):
+    @functools.wraps(f)
+    def inner(self, *args, **kwargs):
+        if self.read_only:
+            raise exceptions.ReadOnlyError('This storage is read-only.')
+        return f(self, *args, **kwargs)
+    return inner
+
+
+class StorageMeta(type):
+    def __init__(cls, name, bases, d):
+        for method in ('update', 'upload', 'delete'):
+            setattr(cls, method, mutating_storage_method(getattr(cls, method)))
+        return super(StorageMeta, cls).__init__(name, bases, d)
+
+
+class Storage(with_metaclass(StorageMeta)):
 
     '''Superclass of all storages, mainly useful to summarize the interface to
     implement.
@@ -63,8 +81,9 @@ class Storage(object):
         if read_only is None:
             read_only = self.read_only
         if self.read_only and not read_only:
-            raise ValueError('This storage is read-only.')
+            raise ValueError('This storage can only be read-only.')
         self.read_only = bool(read_only)
+
         if collection and instance_name:
             instance_name = '{}/{}'.format(instance_name, collection)
         self.instance_name = instance_name
diff --git a/vdirsyncer/utils/compat.py b/vdirsyncer/utils/compat.py
index 20bfd0b..0316c38 100644
--- a/vdirsyncer/utils/compat.py
+++ b/vdirsyncer/utils/compat.py
@@ -27,3 +27,11 @@ else:  # pragma: no cover
     text_type = str
     iteritems = lambda x: x.items()
     itervalues = lambda x: x.values()
+
+
+def with_metaclass(meta, *bases):
+    '''Original code from six, by Benjamin Peterson.'''
+    class metaclass(meta):
+        def __new__(cls, name, this_bases, d):
+            return meta(name, bases, d)
+    return type.__new__(metaclass, 'temporary_class', (), {})