diff --git a/lib/identity_cache/cache_fetcher.rb b/lib/identity_cache/cache_fetcher.rb
index 7122b934..4ed1b7f7 100644
--- a/lib/identity_cache/cache_fetcher.rb
+++ b/lib/identity_cache/cache_fetcher.rb
@@ -234,7 +234,8 @@ def fallback_key_expiration_options(fill_lock_duration)
       # the cache store round down with `to_i`
       expires_in = expires_in.ceil
 
-      # memcached TTL only gets part of the first second, so increase TTL by 1 to compensate
+      # memcached TTL only gets part of the first second (https://github.com/memcached/memcached/issues/307),
+      # so increase TTL by 1 to compensate
       expires_in += 1
 
       { expires_in: expires_in }