diff --git a/src/calibre/gui2/dialogs/choose_library.py b/src/calibre/gui2/dialogs/choose_library.py
index d656a93b6d..abf7fffaed 100644
--- a/src/calibre/gui2/dialogs/choose_library.py
+++ b/src/calibre/gui2/dialogs/choose_library.py
@@ -10,7 +10,7 @@ import os
 from PyQt4.Qt import QDialog
 
 from calibre.gui2.dialogs.choose_library_ui import Ui_Dialog
-from calibre.gui2 import error_dialog, choose_dir
+from calibre.gui2 import error_dialog, choose_dir, warning_dialog
 from calibre.constants import filesystem_encoding
 from calibre import isbytestring, patheq
 from calibre.utils.config import prefs
@@ -61,6 +61,12 @@ class ChooseLibrary(QDialog, Ui_Dialog):
         return True
 
     def perform_action(self, ac, loc):
+        if ac in ('new', 'existing'):
+            warning_dialog(self.parent(), _('Custom columns'),
+                    _('If you use custom columns and they differ between '
+                        'libraries, you will have various problems. Best '
+                        'to ensure you have the same custom columns in each '
+                        'library.'), show=True)
         if ac in ('new', 'existing'):
             prefs['library_path'] = loc
             self.callback(loc)
diff --git a/src/calibre/gui2/layout.py b/src/calibre/gui2/layout.py
index 3116037685..c6885058c0 100644
--- a/src/calibre/gui2/layout.py
+++ b/src/calibre/gui2/layout.py
@@ -83,7 +83,7 @@ class LocationManager(QObject): # {{{
 
         ac('library', _('Library'), 'lt.png',
                 _('Show books in calibre library'))
-        ac('main', _('Main'), 'reader.svg',
+        ac('main', _('Reader'), 'reader.svg',
                 _('Show books in the main memory of the device'))
         ac('carda', _('Card A'), 'sd.svg',
                 _('Show books in storage card A'))