diff --git a/lib/manifesto.rb b/lib/manifesto.rb
index 9ab3b17..eb91f6a 100644
--- a/lib/manifesto.rb
+++ b/lib/manifesto.rb
@@ -30,7 +30,7 @@ def self.cache(options = {})
       # files in the manifest.
       if File.file?(path) && File.basename(path)[0,1] != '.'
         if timestamp
-          manifest << "#{normalize_path(directory, path)}?#{File.mtime(path).to_i.to_s}\n"
+          manifest << "#{normalize_path(directory, path)}?#{get_timestamp(path)}\n"
         else
           manifest << "#{normalize_path(directory, path)}\n"
         end
@@ -71,6 +71,11 @@ def self.normalize_path(directory, path)
     normalized_path = '/' + normalized_path unless normalized_path[0,1] == '/'
     normalized_path
   end
+
+  # Calculates the timestamp for a given file using same methodology as Rails' asset timestamps.
+  def self.get_timestamp(path)
+    File.mtime(path).to_i.to_s
+  end
   
   # Checks that the options passed to the <tt>cache</tt> method are valid.
   def self.validate_options(directory, compute_hash, timestamp)
diff --git a/spec/manifesto_spec.rb b/spec/manifesto_spec.rb
index 8abc5f6..75dddc5 100644
--- a/spec/manifesto_spec.rb
+++ b/spec/manifesto_spec.rb
@@ -3,11 +3,15 @@
 describe Manifesto do
   describe ".validate_options" do
     it "should raise ArgumentError if directory is not a real directory" do
-      expect{ Manifesto.validate_options('', false) }.to raise_error(ArgumentError)
+      expect{ Manifesto.validate_options('', false, false) }.to raise_error(ArgumentError)
     end
 
     it "should raise ArgumentError if compute_hash is not a boolean" do
-      expect{ Manifesto.validate_options('.', nil) }.to raise_error(ArgumentError)
+      expect{ Manifesto.validate_options('.', nil, false) }.to raise_error(ArgumentError)
+    end
+
+    it "should raise ArgumentError if timestamp is not a boolean" do
+      expect{ Manifesto.validate_options('.', false, nil) }.to raise_error(ArgumentError)
     end
   end
 
@@ -40,6 +44,11 @@
         Manifesto.stub!(:get_file_paths).and_return([])
       end
 
+      it "should not get the timestamp" do
+        Manifesto.should_receive(:get_timestamp).never
+        Manifesto.cache
+      end
+
       it "should not compute hash" do
         Manifesto.should_receive(:compute_file_contents_hash).never
         Manifesto.cache
@@ -58,6 +67,11 @@
           File.stub!(:file?).and_return(false)
         end
 
+        it "should not get the timestamp" do
+          Manifesto.should_receive(:get_timestamp).never
+          Manifesto.cache
+        end
+
         it "should not compute hash" do
           Manifesto.should_receive(:compute_file_contents_hash).never
           Manifesto.cache
@@ -75,6 +89,11 @@
           File.stub!(:file?).and_return(true)
         end
 
+        it "should not get the timestamp" do
+          Manifesto.should_receive(:get_timestamp).never
+          Manifesto.cache
+        end
+
         it "should not compute hash" do
           Manifesto.should_receive(:compute_file_contents_hash).never
           Manifesto.cache
@@ -93,6 +112,11 @@
           Manifesto.stub!(:compute_file_contents_hash).and_return('asdfsafasdfsdfszxsd')
         end
 
+        it "should get the timestamp" do
+          Manifesto.should_receive(:get_timestamp).and_return('anything')
+          Manifesto.cache
+        end
+
         it "should compute the hash" do
           Manifesto.should_receive(:compute_file_contents_hash).and_return('anything')
           Manifesto.cache