diff --git a/jsduck.gemspec b/jsduck.gemspec
index 2faae26db..77a6c4716 100644
--- a/jsduck.gemspec
+++ b/jsduck.gemspec
@@ -20,11 +20,11 @@ Gem::Specification.new do |s|
 
   s.executables = ["jsduck"]
 
-  s.add_dependency 'rdiscount'
-  s.add_dependency 'json'
-  s.add_dependency 'parallel'
+  s.add_dependency 'rdiscount', '~> 2.1.6'
+  s.add_dependency 'json', '~> 1.8.0'
+  s.add_dependency 'parallel', '~> 0.7.1'
   s.add_dependency 'rkelly-remix', '~> 0.0.2'
-  s.add_dependency 'dimensions'
+  s.add_dependency 'dimensions', '~> 1.2.0'
 
   s.add_development_dependency 'rspec'
   s.add_development_dependency 'rake'