diff --git a/skimage/io/collection.py b/skimage/io/collection.py
index da2bfda8..dccd88c8 100644
--- a/skimage/io/collection.py
+++ b/skimage/io/collection.py
@@ -254,7 +254,7 @@ class ImageCollection(object):
             if ((self.conserve_memory and n != self._cached) or
                     (self.data[idx] is None)):
                 if self._frame_index:
-                    fname, img_num = self._frame_index[idx]
+                    fname, img_num = self._frame_index[n]
                     self.data[idx] = self.load_func(fname, img_num=img_num,
                                                     **self.load_func_kwargs)
                 else: