diff --git a/proxy/util.coffee b/proxy/util.coffee
index 3cb4ff6a3c2fccd57fe11484a7faca8838babd2d..8f4c75f5b8746227715ec8dc030ed9eba3856420 100644
--- a/proxy/util.coffee
+++ b/proxy/util.coffee
@@ -174,7 +174,7 @@ class BucketRateLimit
 
   # How many seconds in the future will the limit expire?
   when: ->
-    age()
+    @age()
     (@amount - @capacity) / (@capacity / @time)
 
   isLimited: ->