diff --git a/google-apis-generator/google-apis-generator.gemspec b/google-apis-generator/google-apis-generator.gemspec
index 84fa8351a44..aa5d1dfc8b2 100644
--- a/google-apis-generator/google-apis-generator.gemspec
+++ b/google-apis-generator/google-apis-generator.gemspec
@@ -24,5 +24,5 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency "gems", "~> 1.2"
   gem.add_runtime_dependency "google-apis-core", "~> 0.1"
   gem.add_runtime_dependency "google-apis-discovery_v1", "~> 0.0"
-  gem.add_runtime_dependency "thor", "~> 0.20"
+  gem.add_runtime_dependency "thor", ">= 0.20", "< 2.a"
 end