diff --git a/activesupport/lib/active_support/testing/performance.rb b/activesupport/lib/active_support/testing/performance.rb
index 24eea1e40b..6e51dbb735 100644
--- a/activesupport/lib/active_support/testing/performance.rb
+++ b/activesupport/lib/active_support/testing/performance.rb
@@ -319,7 +319,7 @@ begin
 
             def initialize(*args)
               # FIXME: yeah my CPU is 2.33 GHz
-              RubyProf.cpu_frequency = 2.33e9
+              RubyProf.cpu_frequency = 2.33e9 unless RubyProf.cpu_frequency > 0
               super
             end
 
@@ -452,4 +452,4 @@ begin
     end
   end
 rescue LoadError
-end
\ No newline at end of file
+end