diff --git a/lib/bench_press/report.rb b/lib/bench_press/report.rb
index 2500e53..4e1b021 100644
--- a/lib/bench_press/report.rb
+++ b/lib/bench_press/report.rb
@@ -125,7 +125,7 @@ def spacer
     end
 
     def formatted_number(number, delimiter = ',')
-      number.to_s.gsub!(/(\d)(?=(\d\d\d)+(?!\d))/, "\\1#{delimiter}")
+      number.to_s.gsub(/(\d)(?=(\d\d\d)+(?!\d))/, "\\1#{delimiter}")
     end
 
     def run_name(content)
diff --git a/spec/bench_press/report_spec.rb b/spec/bench_press/report_spec.rb
index 12a00f7..28349c6 100644
--- a/spec/bench_press/report_spec.rb
+++ b/spec/bench_press/report_spec.rb
@@ -43,6 +43,10 @@
     it "comma-separates a number" do
       subject.send(:formatted_number, 1000000).should == "1,000,000"
     end
+
+    it "does not change numbers below 1000" do
+      subject.send(:formatted_number, 999).should == "999"
+    end
   end
 
   describe "#runnable_results" do