diff --git a/lib/mspec/matchers/match_yaml.rb b/lib/mspec/matchers/match_yaml.rb
index 664ca73..3056162 100644
--- a/lib/mspec/matchers/match_yaml.rb
+++ b/lib/mspec/matchers/match_yaml.rb
@@ -30,7 +30,7 @@ def clean_yaml(yaml)
   def valid_yaml?(obj)
     require 'yaml'
     begin
-      if defined?(YAML.unsafe_load)
+      if YAML.respond_to?(:unsafe_load)
         YAML.unsafe_load(obj)
       else
         YAML.load(obj)