diff --git a/src/spec.coffee b/src/spec.coffee
index f3e58c60b..2ec2b32ef 100644
--- a/src/spec.coffee
+++ b/src/spec.coffee
@@ -22,7 +22,7 @@ module.exports = (refsToUUIDs) ->
       helper = (value) ->
         if value instanceof Array
           (helper value_ for value_ in value)
-        else if refsToUUIDs[value]
+        else if refsToUUIDs[value] isnt undefined
           refsToUUIDs[value]
         else
           value