diff --git a/Gemfile.lock b/Gemfile.lock
index 2b9acab..a0385f7 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -12,7 +12,7 @@ GEM
     rake (10.1.0)
     rake-compiler (0.9.2)
       rake
-    rdoc (4.0.1)
+    rdoc (3.12.2)
       json (~> 1.4)
     rspec (2.14.1)
       rspec-core (~> 2.14.0)
@@ -30,5 +30,5 @@ PLATFORMS
 DEPENDENCIES
   bcrypt!
   rake-compiler (~> 0.9.2)
-  rdoc
+  rdoc (~> 3.12)
   rspec
diff --git a/bcrypt.gemspec b/bcrypt.gemspec
index b658db7..333c582 100644
--- a/bcrypt.gemspec
+++ b/bcrypt.gemspec
@@ -14,7 +14,7 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency 'rake-compiler', '~> 0.9.2'
   s.add_development_dependency 'rspec'
-  s.add_development_dependency 'rdoc'
+  s.add_development_dependency 'rdoc', '~> 3.12'
 
   s.has_rdoc = true
   s.rdoc_options += ['--title', 'bcrypt-ruby', '--line-numbers', '--inline-source', '--main', 'README.md']