diff --git a/mongo-extensions.gemspec b/mongo-extensions.gemspec
index b27fae9..f2123bf 100644
--- a/mongo-extensions.gemspec
+++ b/mongo-extensions.gemspec
@@ -9,6 +9,8 @@ Gem::Specification.new do |s|
   s.name = 'mongo_ext'
 
   s.version = '0.15'
+  s.add_dependency('mongo', ['= 0.15'])
+
   s.platform = Gem::Platform::RUBY
   s.summary = 'C extensions for the MongoDB Ruby driver'
   s.description = 'C extensions to accelerate the MongoDB Ruby driver. For more information about Mongo, see http://www.mongodb.org.'