diff --git a/lib/origin/mergeable.rb b/lib/origin/mergeable.rb
index 9d7eab6..3493987 100644
--- a/lib/origin/mergeable.rb
+++ b/lib/origin/mergeable.rb
@@ -150,7 +150,9 @@ def __multi__(criterion, operator)
           next unless expr
           criteria = sel[operator] || []
           normalized = expr.inject({}) do |hash, (field, value)|
-            hash.merge!(field.__expr_part__(value.__expand_complex__))
+            hash.merge!(field.__expr_part__(value.__expand_complex__)) do |_, existing, additional|
+              existing.merge(additional)
+            end
             hash
           end
           sel.store(operator, criteria.push(normalized))