diff --git a/tumugi-plugin-google_drive.gemspec b/tumugi-plugin-google_drive.gemspec
index 6eae131..a8a88a5 100644
--- a/tumugi-plugin-google_drive.gemspec
+++ b/tumugi-plugin-google_drive.gemspec
@@ -19,8 +19,9 @@ Gem::Specification.new do |spec|
 
   spec.required_ruby_version = '>= 2.1'
 
-  spec.add_runtime_dependency "tumugi", ">= 0.5.1"
+  spec.add_runtime_dependency "tumugi", "~> 0.6.1"
   spec.add_runtime_dependency "google-api-client", "~> 0.9.3"
+  spec.add_runtime_dependency "json", "~> 1.8.3" # json 2.0 does not work with JRuby + MultiJson
 
   spec.add_development_dependency "bundler", "~> 1.11"
   spec.add_development_dependency "rake", "~> 10.0"