diff --git a/modules/simpletest/tests/upgrade/drupal-6.user-password-token.database.php b/modules/simpletest/tests/upgrade/drupal-6.user-password-token.database.php
index 367c704..e91b6e4 100644
--- a/modules/simpletest/tests/upgrade/drupal-6.user-password-token.database.php
+++ b/modules/simpletest/tests/upgrade/drupal-6.user-password-token.database.php
@@ -8,3 +8,48 @@ db_insert('variable')->fields(array(
   'value' => 's:97:"!password, !username, !site, !uri, !uri_brief, !mailto, !date, !login_uri, !edit_uri, !login_url.";',
 ))
 ->execute();
+
+db_insert('users')->fields(array(
+  'uid',
+  'name',
+  'pass',
+  'mail',
+  'mode',
+  'sort',
+  'threshold',
+  'theme',
+  'signature',
+  'signature_format',
+  'created',
+  'access',
+  'login',
+  'status',
+  'timezone',
+  'language',
+  'picture',
+  'init',
+  'data',
+))
+->values(array(
+  'uid' => 3,
+  'name' => 'hashtester',
+  // This is not a valid D7 hash, but a truncated one.
+  'pass' => '$S$DAK00p3Dkojkf4O/UizYxenguXnjv',
+  'mail' => 'hashtester@example.com',
+  'mode' => '0',
+  'sort' => '0',
+  'threshold' => '0',
+  'theme' => '',
+  'signature' => '',
+  'signature_format' => '0',
+  'created' => '1277671599',
+  'access' => '1277671612',
+  'login' => '1277671612',
+  'status' => '1',
+  'timezone' => '-21600',
+  'language' => '',
+  'picture' => '',
+  'init' => 'hashtester@example.com',
+  'data' => 'a:0:{}',
+))
+->execute();
diff --git a/modules/simpletest/tests/upgrade/upgrade.user.test b/modules/simpletest/tests/upgrade/upgrade.user.test
index 6c66921..c33ba11 100644
--- a/modules/simpletest/tests/upgrade/upgrade.user.test
+++ b/modules/simpletest/tests/upgrade/upgrade.user.test
@@ -26,6 +26,9 @@ class UserUpgradePathPasswordTokenTestCase extends UpgradePathTestCase {
   public function testUserUpgrade() {
     $this->assertTrue($this->performUpgrade(), 'The upgrade was completed successfully.');
     $this->assertEqual(variable_get('user_mail_register_no_approval_required_body'), ', [user:name], [site:name], [site:url], [site:url-brief], [user:mail], [date:medium], [site:login-url], [user:edit-url], [user:one-time-login-url].', 'Existing email templates have been modified (password token involved).');
+    // Check that a non-md5 hash was untouched.
+    $pass = db_query('SELECT pass FROM {users} WHERE uid = 3')->fetchField();
+    $this->assertEqual('$S$DAK00p3Dkojkf4O/UizYxenguXnjv', $pass, 'Pre-existing non-MD5 password hash was not altered');
   }
 }
 
diff --git a/modules/user/user.install b/modules/user/user.install
index 9d855ea..9119aac 100644
--- a/modules/user/user.install
+++ b/modules/user/user.install
@@ -428,6 +428,13 @@ function user_update_7000(&$sandbox) {
     $result = db_query_range("SELECT uid, pass FROM {users} WHERE uid > 0 ORDER BY uid", $sandbox['user_from'], $count);
     foreach ($result as $account) {
       $has_rows = TRUE;
+
+      // If the $account->pass value is not a MD5 hash (a 32 character
+      // hexadecimal string) then skip it.
+      if (!preg_match('/^[0-9a-f]{32}$/', $account->pass)) {
+        continue;
+      }
+
       $new_hash = user_hash_password($account->pass, $hash_count_log2);
       if ($new_hash) {
         // Indicate an updated password.