diff --git a/.travis_build_config.rb b/.travis_build_config.rb
index c873319..769b98a 100644
--- a/.travis_build_config.rb
+++ b/.travis_build_config.rb
@@ -1,5 +1,6 @@
 MRuby::Build.new do |conf|
   toolchain :gcc
+  enable_debug
   conf.gembox 'default'
   conf.gem '../mruby-method'
 end
diff --git a/README.md b/README.md
index 6d301fa..c8c88b5 100644
--- a/README.md
+++ b/README.md
@@ -11,3 +11,13 @@ p Enumerable.instance_method(:find_all).source_location
 ```
 
 ![https://raw.githubusercontent.com/ksss/mruby-method/master/find_all.png](https://raw.githubusercontent.com/ksss/mruby-method/master/find_all.png)
+
+# Note
+
+`source_location` method need this configuration in build_config.rb
+
+```
+MRuby::Build.new do |conf|
+  enable_debug
+end
+```