diff --git a/lib/logstash/codecs/json_lines.rb b/lib/logstash/codecs/json_lines.rb
index 2190a45..c917b93 100644
--- a/lib/logstash/codecs/json_lines.rb
+++ b/lib/logstash/codecs/json_lines.rb
@@ -34,32 +34,18 @@ def register
     @buffer = FileWatch::BufferedTokenizer.new(@delimiter)
     @converter = LogStash::Util::Charset.new(@charset)
     @converter.logger = @logger
-
-    # pick the correct parser here and not at class evaluation so that we can control this
-    # mechanism in rspec and actually force use both strategies.
-    self.class.module_eval do
-      # keep compatibility with all v2.x distributions. only in 2.3 will the Event#from_json method be introduced
-      # and we need to keep compatibility for all v2 releases.
-      alias_method :parse, from_json_exposed? ? :from_json_parse : :legacy_parse
-    end
   end
 
   def decode(data, &block)
     @buffer.extract(data).each do |line|
       parse(@converter.convert(line), &block)
     end
-  end # def decode
+  end
 
   def encode(event)
     # Tack on a @delimiter for now because previously most of logstash's JSON
     # outputs emitted one per line, and whitespace is OK in json.
     @on_event.call(event, "#{event.to_json}#{@delimiter}")
-  end # def encode
-
-  # this method is made public to that we can mock it in rspec and control
-  # testing using from_json or legacy mechanism.
-  def self.from_json_exposed?
-    LogStash::Event.respond_to?(:from_json)
   end
 
   private
@@ -77,4 +63,7 @@ def legacy_parse(json, &block)
   rescue LogStash::Json::ParserError
     yield LogStash::Event.new("message" => json, "tags" => ["_jsonparsefailure"])
   end
+
+  alias_method :parse, LogStash::Event.respond_to?(:from_json) ? :from_json_parse : :legacy_parse
+
 end # class LogStash::Codecs::JSONLines
diff --git a/spec/codecs/json_lines_spec.rb b/spec/codecs/json_lines_spec.rb
index 0aadbd1..ae2e186 100644
--- a/spec/codecs/json_lines_spec.rb
+++ b/spec/codecs/json_lines_spec.rb
@@ -173,10 +173,18 @@
   context "forcing legacy parsing" do
     it_behaves_like :codec do
       subject do
-        expect(LogStash::Codecs::JSONLines).to receive(:from_json_exposed?).and_return(false)
         # register method is called in the constructor
         LogStash::Codecs::JSONLines.new(codec_options)
       end
+
+      before(:each) do
+        # stub codec parse method to force use of the legacy parser.
+        # this is very implementation specific but I am not sure how
+        # this can be tested otherwise.
+        allow(subject).to receive(:parse) do |line, &block|
+          subject.send(:legacy_parse, line, &block)
+        end
+      end
     end
   end