diff --git a/lib/bud.rb b/lib/bud.rb
index <HASH>..<HASH> 100644
--- a/lib/bud.rb
+++ b/lib/bud.rb
@@ -843,8 +843,8 @@ module Bud
         next if coll.nil?
 
         unless coll.delta.empty? and coll.new_delta.empty?
+          fixpoint = false unless coll.new_delta.empty?
           coll.tick_deltas
-          fixpoint = false
         end
       end
     end while not fixpoint
Tweak fixpoint logic.

When computing a per-stratum fixpoint, we only need to rerun the stratum if at
least one relation in the stratum has a non-empty @new_delta field. The previous
coding also reran the stratum if any relation had a non-empty @delta field,
which is unnecessary: the consequences of @delta tuples should already be
computed.