diff --git a/activesupport/lib/active_support/number_helper/number_to_delimited_converter.rb b/activesupport/lib/active_support/number_helper/number_to_delimited_converter.rb
index 45ae8f1a93..43c5540b6f 100644
--- a/activesupport/lib/active_support/number_helper/number_to_delimited_converter.rb
+++ b/activesupport/lib/active_support/number_helper/number_to_delimited_converter.rb
@@ -12,7 +12,7 @@ module ActiveSupport
       private
 
         def parts
-          left, right = number.to_s.split('.')
+          left, right = number.to_s.split('.'.freeze)
           left.gsub!(delimiter_pattern) do |digit_to_delimit|
             "#{digit_to_delimit}#{options[:delimiter]}"
           end
diff --git a/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb b/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb
index 981c562551..9fb7dfb779 100644
--- a/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb
+++ b/activesupport/lib/active_support/number_helper/number_to_rounded_converter.rb
@@ -29,9 +29,11 @@ module ActiveSupport
 
           formatted_string =
             if BigDecimal === rounded_number && rounded_number.finite?
-              s = rounded_number.to_s('F') + '0'*precision
-              a, b = s.split('.', 2)
-              a + '.' + b[0, precision]
+              s = rounded_number.to_s('F')
+              s << '0'.freeze * precision
+              a, b = s.split('.'.freeze, 2)
+              a << '.'.freeze
+              a << b[0, precision]
             else
               "%00.#{precision}f" % rounded_number
             end