diff --git a/wcs_olap/feeder.py b/wcs_olap/feeder.py
index 614b574..9cf58a1 100644
--- a/wcs_olap/feeder.py
+++ b/wcs_olap/feeder.py
@@ -817,7 +817,10 @@ class WcsFormdefFeeder(object):
                 except KeyError:
                     v = None
                 else:
-                    v = v and self.olap_feeder.role_mapping[v.id]
+                    if v and v.id in self.olap_feeder.role_mapping:
+                        v = self.olap_feeder.role_mapping[v.id]
+                    else:
+                        v = None
                 at = 'function_%s' % slugify(function)
                 row[at] = v