diff --git a/features/sync_gemfile.feature b/features/sync_gemfile.feature
index 1b1ed8a..d5f91ce 100644
--- a/features/sync_gemfile.feature
+++ b/features/sync_gemfile.feature
@@ -51,4 +51,19 @@ Feature: sync a Gemfile between two repositories
       gem "postgresql"
       >>>>>>> .trout/upstream
       """
-
+    When I write to "Gemfile" with:
+      """
+      source "http://rubygems.org"
+      gem "rails"
+      gem "mysql"
+      gem "redcloth"
+      """
+    When I run "trout update Gemfile"
+    And I run "cat Gemfile"
+    Then the output should contain:
+      """
+      source "http://rubygems.org"
+      gem "rails"
+      gem "mysql"
+      gem "redcloth"
+      """
diff --git a/lib/trout/managed_file.rb b/lib/trout/managed_file.rb
index b3d8b26..6cd310f 100644
--- a/lib/trout/managed_file.rb
+++ b/lib/trout/managed_file.rb
@@ -19,7 +19,10 @@ def copy_from(git_url)
 
     def update
       checkout(previous_git_url)
-      merge_to_destination
+      unless up_to_date?
+        merge_to_destination
+        write_url_and_version
+      end
     ensure
       cleanup
     end
@@ -76,7 +79,7 @@ def write_url_and_version
     end
 
     def checked_out_version
-      git_command("rev-parse HEAD")
+      git_command("rev-parse master")
     end
 
     def checkout_last_version
@@ -95,6 +98,10 @@ def previous_git_version
       version_list.version_for(filename)
     end
 
+    def up_to_date?
+      previous_git_version == checked_out_version
+    end
+
     def version_list
       @version_list ||= VersionList.new(working('versions'))
     end