diff --git a/lib/jekyll/filters.rb b/lib/jekyll/filters.rb
index 37d4f1cb..1886194b 100644
--- a/lib/jekyll/filters.rb
+++ b/lib/jekyll/filters.rb
@@ -30,7 +30,7 @@ module Jekyll
     #
     # Returns the formatting String.
     def date_to_string(date)
-      date.strftime("%d %b %Y")
+      time(date).strftime("%d %b %Y")
     end
 
     # Format a date in long format e.g. "27 January 2011".
@@ -39,7 +39,7 @@ module Jekyll
     #
     # Returns the formatted String.
     def date_to_long_string(date)
-      date.strftime("%d %B %Y")
+      time(date).strftime("%d %B %Y")
     end
 
     # Format a date for use in XML.
@@ -53,7 +53,7 @@ module Jekyll
     #
     # Returns the formatted String.
     def date_to_xmlschema(date)
-      date.xmlschema
+      time(date).xmlschema
     end
 
     # Format a date according to RFC-822
@@ -67,7 +67,7 @@ module Jekyll
     #
     # Returns the formatted String.
     def date_to_rfc822(date)
-      date.rfc822
+      time(date).rfc822
     end
 
     # XML escape a string for use. Replaces any special characters with
@@ -137,5 +137,18 @@ module Jekyll
         "#{array[0...-1].join(', ')}, #{connector} #{array[-1]}"
       end
     end
+
+    private
+    def time(input)
+      case input
+      when Time
+        input
+      when String
+        Time.parse(input)
+      else
+        Jekyll::Logger.error "Invalid Date:", "'#{input}' is not a valid datetime."
+        exit(1)
+      end
+    end
   end
 end