diff --git a/vdirsyncer/cli/config.py b/vdirsyncer/cli/config.py
index 9a909b2..3a95645 100644
--- a/vdirsyncer/cli/config.py
+++ b/vdirsyncer/cli/config.py
@@ -7,6 +7,7 @@ from click_threading import get_ui_worker
 
 from . import cli_logger
 from .fetchparams import expand_fetch_params
+from .utils import storage_class_from_config
 from .. import PROJECT_HOME, exceptions
 from ..utils import expand_path
 
@@ -287,11 +288,16 @@ class PairConfig(object):
 
     def _set_partial_sync(self, options):
         partial_sync = options.pop('partial_sync', None)
-        if partial_sync is not None and \
-           not self.config_a.get('read_only', False) and \
-           not self.config_b.get('read_only', False):
-            raise ValueError('`partial_sync` is only effective if one storage '
-                             'is read-only.')
+        if partial_sync is not None:
+           cls_a, _  = storage_class_from_config(self.config_a)
+           cls_b, _  = storage_class_from_config(self.config_b)
+
+           if not cls_a.read_only and \
+              not self.config_a.get('read_only', False) and \
+              not cls_b.read_only and \
+              not self.config_b.get('read_only', False):
+                raise ValueError('`partial_sync` is only effective if one '
+                                 'storage is read-only.')
 
         if partial_sync is None:
             partial_sync = 'revert'