diff --git a/js/entity_browser.common.js b/js/entity_browser.common.js
index d28e176..357635e 100644
--- a/js/entity_browser.common.js
+++ b/js/entity_browser.common.js
@@ -106,6 +106,9 @@
       combined_entities = existing_entities.concat(selected_entities);
     }
 
+    // Ensure unique entities are selected.
+    combined_entities = _.unique(combined_entities);
+
     // Having more elements than cardinality should never happen, because
     // server side authentication should prevent it, but we handle it here
     // anyway.