diff --git a/lib/mutant/runner.rb b/lib/mutant/runner.rb
index 50bab7b9..65233419 100644
--- a/lib/mutant/runner.rb
+++ b/lib/mutant/runner.rb
@@ -14,7 +14,7 @@ module Mutant
     # @api private
     #
     def self.register(klass)
-      REGISTRY[klass]=self
+      REGISTRY[klass] = self
     end
     private_class_method :register