diff --git a/logstash-core/lib/logstash/compiler/lscl.rb b/logstash-core/lib/logstash/compiler/lscl.rb
index 277c3ef27..b4cdb4d0d 100644
--- a/logstash-core/lib/logstash/compiler/lscl.rb
+++ b/logstash-core/lib/logstash/compiler/lscl.rb
@@ -115,7 +115,7 @@ module LogStashCompilerLSCLGrammar; module LogStash; module Compiler; module LSC
         elsif existing.kind_of?(::Array)
           hash[k] = existing.push(*v)
         else
-          hash[k] = existing + v
+          hash[k] = [existing, v] unless v == existing
         end
         hash
       end