2 files changed, 5 insertions, 4 deletions
diff --git a/activesupport/lib/active_support/core_ext/time/calculations.rb b/activesupport/lib/active_support/core_ext/time/calculations.rb
index a0f610d60c..92b8417150 100644
--- a/activesupport/lib/active_support/core_ext/time/calculations.rb
+++ b/activesupport/lib/active_support/core_ext/time/calculations.rb
@@ -253,7 +253,7 @@ class Time
       :hour => 23,
       :min => 59,
       :sec => 59,
-      :usec => 999999.999
+      :usec => Rational(999999999, 1000)
     )
   end
 
@@ -268,7 +268,7 @@ class Time
     change(
       :min => 59,
       :sec => 59,
-      :usec => 999999.999
+      :usec => Rational(999999999, 1000)
     )
   end
 
@@ -288,7 +288,7 @@ class Time
       :hour => 23,
       :min  => 59,
       :sec  => 59,
-      :usec => 999999.999
+      :usec => Rational(999999999, 1000)
     )
   end
   alias :at_end_of_month :end_of_month
@@ -321,7 +321,7 @@ class Time
       :hour  => 23,
       :min   => 59,
       :sec   => 59,
-      :usec  => 999999.999
+      :usec  => Rational(999999999, 1000)
     )
   end
   alias :at_end_of_year :end_of_year
diff --git a/activesupport/lib/active_support/core_ext/time/conversions.rb b/activesupport/lib/active_support/core_ext/time/conversions.rb
index 4f852fd780..10ca26acf2 100644
--- a/activesupport/lib/active_support/core_ext/time/conversions.rb
+++ b/activesupport/lib/active_support/core_ext/time/conversions.rb
@@ -5,6 +5,7 @@ class Time
   DATE_FORMATS = {
     :db           => '%Y-%m-%d %H:%M:%S',
     :number       => '%Y%m%d%H%M%S',
+    :nsec         => '%Y%m%d%H%M%S%9N',
     :time         => '%H:%M',
     :short        => '%d %b %H:%M',
     :long         => '%B %d, %Y %H:%M',