diff --git a/GPy/util/caching.py b/GPy/util/caching.py
index c8cf7149..583cb26f 100644
--- a/GPy/util/caching.py
+++ b/GPy/util/caching.py
@@ -119,7 +119,7 @@ class Cacher(object):
         """
         Totally reset the cache
         """
-        [a().remove_observer(self, self.on_cache_changed) if (a() is not None) else None for a in self.cached_input_ids.values()]
+        [a().remove_observer(self, self.on_cache_changed) if (a() is not None) else None for [a, _] in self.cached_input_ids.values()]
         self.cached_input_ids = {}
         self.cached_outputs = {}
         self.inputs_changed = {}