diff --git a/grn.drush.inc b/grn.drush.inc
index bc41fc1..eacec09 100644
--- a/grn.drush.inc
+++ b/grn.drush.inc
@@ -65,7 +65,7 @@ function grn_drush_command() {
 /**
  * Implements drush_hook_COMMAND().
  */
-function drush_grn_release_notes($tag1n, $tag2n) {
+function drush_grn_release_notes($tag1n = NULL, $tag2n = NULL) {
   $git = 'git';
   if (drush_get_option('git')) {
     $git = drush_get_option('git');
@@ -74,6 +74,18 @@ function drush_grn_release_notes($tag1n, $tag2n) {
   if (!is_dir(".git")) {
     drush_log("This must be run from the root directory of your Git project.");
   }
+
+  // If no tags are provided, use the two most recent ones.
+  if (!isset($tag1n) && !isset($tag2n)) {
+    // Get all the defined tags in this repository and sort them.
+    drush_shell_exec('%s tag', $git);
+    $tags = drush_shell_exec_output();
+    uasort($tags, 'version_compare');
+
+    $tag2n = array_pop($tags);
+    $tag1n = array_pop($tags);
+  }
+
   // '^' is the escape character on Windows (like '\' on *nix) - has to be
   // contained in the escaped shell argument string ("%s").
   if (!drush_shell_exec('%s show -s --pretty=format:%%H %s', $git, $tag1n . '^{commit}')) {