diff --git a/chxtools/pims_readers/eiger.py b/chxtools/pims_readers/eiger.py
index 1a83540..0693f2f 100644
--- a/chxtools/pims_readers/eiger.py
+++ b/chxtools/pims_readers/eiger.py
@@ -55,8 +55,8 @@ def __init__(self, master_filepath):
         # Table of Contents return a tuple:
         # self._toc[5] -> [which file, which element in that file]
         self._toc = np.concatenate(
-                [zip(i*np.ones(length, dtype=int),
-                     np.arange(length, dtype=int))
+                [list(zip(i*np.ones(length, dtype=int),
+                     np.arange(length, dtype=int)))
                 for i, length in enumerate(lengths)])
 
     def get_frame(self, i):