diff --git a/config/flay.yml b/config/flay.yml
index a210fa14..c9552bb0 100644
--- a/config/flay.yml
+++ b/config/flay.yml
@@ -1,3 +1,3 @@
 ---
 threshold: 16
-total_score: 607
+total_score: 604
diff --git a/lib/mutant.rb b/lib/mutant.rb
index 71b56788..fb5a5db0 100644
--- a/lib/mutant.rb
+++ b/lib/mutant.rb
@@ -1,3 +1,4 @@
+require 'benchmark'
 require 'set'
 require 'adamantium'
 require 'ice_nine'
diff --git a/lib/mutant/killer.rb b/lib/mutant/killer.rb
index 46280148..282206b6 100644
--- a/lib/mutant/killer.rb
+++ b/lib/mutant/killer.rb
@@ -89,10 +89,10 @@ module Mutant
     # @api private
     #
     def run_with_benchmark
-      start_time = Time.now
-      @killed = run
-      end_time = Time.now
-      @runtime = end_time - start_time
+      times = Benchmark.measure do
+        @killed = run
+      end
+      @runtime = times.real
     end
 
     # Run killer