diff --git a/mutant.gemspec b/mutant.gemspec
index 9f8b9145..5124969f 100644
--- a/mutant.gemspec
+++ b/mutant.gemspec
@@ -16,7 +16,7 @@ Gem::Specification.new do |gem|
   gem.executables       = [ 'mutant' ]
 
   gem.add_runtime_dependency('backports',           [ '~> 3.0', '>= 3.0.3' ])
-  gem.add_runtime_dependency('to_source',           '~> 0.2.14')
+  gem.add_runtime_dependency('to_source',           '~> 0.2.20')
   gem.add_runtime_dependency('ice_nine',            '~> 0.7.0')
   gem.add_runtime_dependency('descendants_tracker', '~> 0.0.1')
   gem.add_runtime_dependency('adamantium',          '~> 0.0.7')