diff --git a/src/calibre/devices/prs500/driver.py b/src/calibre/devices/prs500/driver.py
index cb7cd715fd..0e9bb58f3e 100644
--- a/src/calibre/devices/prs500/driver.py
+++ b/src/calibre/devices/prs500/driver.py
@@ -865,7 +865,7 @@ class PRS500(DeviceConfig, DevicePlugin):
         size = sum(sizes)
         space = self.free_space(end_session=False)
         mspace = space[0]
-        cspace = space[1] if space[1] >= space[2] else space[2]
+        cspace = space[2] if len(space) > 2 and space[2] >= space[1] else  space[1]
         if on_card and size > cspace - 1024*1024:
             raise FreeSpaceError("There is insufficient free space "+\
                                           "on the storage card")
diff --git a/src/calibre/gui2/widgets.py b/src/calibre/gui2/widgets.py
index e25dfc7870..b2d318b981 100644
--- a/src/calibre/gui2/widgets.py
+++ b/src/calibre/gui2/widgets.py
@@ -216,6 +216,12 @@ class LocationModel(QAbstractListModel):
         return NONE
 
     def update_devices(self, cp=(None, None), fs=[-1, -1, -1]):
+        if cp is None:
+            cp = (None, None)
+        if isinstance(cp, (str, unicode)):
+            cp = (cp, None)
+        if len(fs) < 3:
+            fs = list(fs) + [0]
         self.free[0] = fs[0]
         self.free[1] = fs[1]
         self.free[2] = fs[2]