diff --git a/mutant.gemspec b/mutant.gemspec
index 240a0027..a85f15db 100644
--- a/mutant.gemspec
+++ b/mutant.gemspec
@@ -15,7 +15,7 @@ Gem::Specification.new do |gem|
   gem.extra_rdoc_files = %w[TODO]
   gem.executables       = [ 'mutant' ]
 
-  gem.add_runtime_dependency('to_source',           '~> 0.2.1')
+  gem.add_runtime_dependency('to_source',           '~> 0.2.3')
   gem.add_runtime_dependency('ice_nine',            '~> 0.5.0')
   gem.add_runtime_dependency('descendants_tracker', '~> 0.0.1')
   gem.add_runtime_dependency('backports',           '~> 2.6')