diff --git a/lib/rspec/json_expectations/matcher_factory.rb b/lib/rspec/json_expectations/matcher_factory.rb
index bd0da9e..6a125b5 100644
--- a/lib/rspec/json_expectations/matcher_factory.rb
+++ b/lib/rspec/json_expectations/matcher_factory.rb
@@ -7,7 +7,7 @@ def initialize(matcher_name)
 
       def define_matcher(&block)
         RSpec::Matchers.define(@matcher_name) do |expected|
-          yield
+          self.module_eval(&block)
 
           match do |actual|
             traverse(expected, actual, false)