diff --git a/odoo/addons/base/module/module.py b/odoo/addons/base/module/module.py
index 233d12cb370..4d3e859352b 100644
--- a/odoo/addons/base/module/module.py
+++ b/odoo/addons/base/module/module.py
@@ -643,6 +643,15 @@ class Module(models.Model):
         if not self.env.user.has_group('base.group_system'):
             raise AccessDenied()
 
+        # One-click install is opt-in - cfr Issue #15225
+        ad_dir = tools.config.addons_data_dir
+        if not os.access(ad_dir, os.W_OK):
+            msg = (_("Automatic install of downloaded Apps is currently disabled.") + "\n\n" +
+                   _("To enable it, make sure this directory exists and is writable on the server:") +
+                   "\n%s" % ad_dir)
+            _logger.warning(msg)
+            raise UserError(msg)
+
         apps_server = urlparse.urlparse(self.get_apps_server())
 
         OPENERP = odoo.release.product_name.lower()
diff --git a/odoo/modules/module.py b/odoo/modules/module.py
index 014f2d0ed9b..ecf95be088b 100644
--- a/odoo/modules/module.py
+++ b/odoo/modules/module.py
@@ -128,7 +128,7 @@ def initialize_sys_path():
     global hooked
 
     dd = tools.config.addons_data_dir
-    if dd not in ad_paths:
+    if os.access(dd, os.R_OK) and dd not in ad_paths:
         ad_paths.append(dd)
 
     for ad in tools.config['addons_path'].split(','):
diff --git a/odoo/tools/config.py b/odoo/tools/config.py
index 2473fe53304..fb29d0d4a83 100644
--- a/odoo/tools/config.py
+++ b/odoo/tools/config.py
@@ -582,10 +582,11 @@ class configmanager(object):
     def addons_data_dir(self):
         d = os.path.join(self['data_dir'], 'addons', release.series)
         if not os.path.exists(d):
-            os.makedirs(d, 0700)
-        else:
-            assert os.access(d, os.W_OK), \
-                "%s: directory is not writable" % d
+            try:
+                # try to make +rx placeholder dir, will need manual +w to activate it
+                os.makedirs(d, 0500)
+            except OSError:
+                logging.getLogger(__name__).debug('Failed to create addons data dir %s', d)
         return d
 
     @property