diff --git a/modules/aggregator/aggregator.module b/modules/aggregator/aggregator.module
index d5cf06263706a0ddb83ab0f3ff1d4914d0118de9..16fdf072bea62924f1381a76a2fc23762a1ec27f 100644
--- a/modules/aggregator/aggregator.module
+++ b/modules/aggregator/aggregator.module
@@ -344,7 +344,7 @@ function aggregator_form_category($edit = array()) {
  * Validate aggregator_form_feed form submissions.
  */
 function aggregator_form_category_validate($form_id, $form_values) {
-  if ($_POST['op'] == t('Submit')) {
+  if ($form_values['op'] == t('Submit')) {
     // Check for duplicate titles
     if (isset($form_values['cid'])) {
       $category = db_fetch_object(db_query("SELECT cid FROM {aggregator_category} WHERE title = '%s' AND cid != %d", $form_values['title'], $form_values['cid']));
@@ -363,7 +363,7 @@ function aggregator_form_category_validate($form_id, $form_values) {
  * @todo Add delete confirmation dialog.
  */
 function aggregator_form_category_submit($form_id, $form_values) {
-  if ($_POST['op'] == t('Delete')) {
+  if ($form_values['op'] == t('Delete')) {
     $title = $form_values['title'];
     // Unset the title:
     unset($form_values['title']);
@@ -475,7 +475,7 @@ function aggregator_form_feed($edit = array()) {
  * Validate aggregator_form_feed form submissions.
  */
 function aggregator_form_feed_validate($form_id, $form_values) {
-  if ($_POST['op'] == t('Submit')) {
+  if ($form_values['op'] == t('Submit')) {
     // Check for duplicate titles
     if (isset($form_values['fid'])) {
       $result = db_query("SELECT title, url FROM {aggregator_feed} WHERE (title = '%s' OR url='%s') AND fid != %d", $form_values['title'], $form_values['url'], $form_values['fid']);
@@ -499,7 +499,7 @@ function aggregator_form_feed_validate($form_id, $form_values) {
  * @todo Add delete confirmation dialog.
  */
 function aggregator_form_feed_submit($form_id, $form_values) {
-  if ($_POST['op'] == t('Delete')) {
+  if ($form_values['op'] == t('Delete')) {
     $title = $form_values['title'];
     // Unset the title:
     unset($form_values['title']);
diff --git a/modules/book/book.module b/modules/book/book.module
index 94ca853868cc57de20b947404d47a64565bbd4e9..30969a1cad4cd43873bc9ab0042b8c360f91a90f 100644
--- a/modules/book/book.module
+++ b/modules/book/book.module
@@ -332,7 +332,7 @@ function book_outline($nid) {
  * Handles book outline form submissions.
  */
 function book_outline_submit($form_id, $form_values) {
-  $op = $_POST['op'];
+  $op = $form_values['op'];
   $node = node_load($form_values['nid']);
 
   switch ($op) {
diff --git a/modules/search/search.module b/modules/search/search.module
index d23ef0a4cc20f909e8789098a32103ab89d70657..88bdf5ff65e6c923094aaf3ba2041d371c62c5aa 100644
--- a/modules/search/search.module
+++ b/modules/search/search.module
@@ -200,7 +200,7 @@ function search_menu($may_cache) {
  * Validate callback.
  */
 function search_admin_settings_validate($form_id, $form_values) {
-  if ($_POST['op'] == t('Re-index site')) {
+  if ($form_values['op'] == t('Re-index site')) {
     drupal_goto('admin/settings/search/wipe');
   }
   // If these settings change, the index needs to be rebuilt.
diff --git a/modules/system/system.module b/modules/system/system.module
index c60041ec2cc70a2c3e62eece435a002f87c6372a..a73f69e15778dc742e5d2164b31f4b943e450386 100644
--- a/modules/system/system.module
+++ b/modules/system/system.module
@@ -1106,7 +1106,7 @@ function system_theme_settings_submit($form_id, $form_values) {
  *
  */
 function system_settings_form_submit($form_id, $form_values) {
-  $op = isset($_POST['op']) ? $_POST['op'] : '';
+  $op = isset($form_values['op']) ? $form_values['op'] : '';
 
   // Exclude unnecessary elements.
   unset($form_values['submit'], $form_values['reset'], $form_values['form_id']);
@@ -1191,7 +1191,7 @@ function system_themes_submit($form_id, $form_values) {
 
   db_query("UPDATE {system} SET status = 0 WHERE type = 'theme'");
 
-  if ($_POST['op'] == t('Save configuration')) {
+  if ($form_values['op'] == t('Save configuration')) {
     if (is_array($form_values['status'])) {
       foreach ($form_values['status'] as $key => $choice) {
         // Always enable the default theme, despite its status checkbox being checked:
diff --git a/modules/user/user.module b/modules/user/user.module
index ce76468dfa45959b3ae0318d49d344687604e8d8..a545c505f480a6ea58e1189e0cf95d796c9e7557 100644
--- a/modules/user/user.module
+++ b/modules/user/user.module
@@ -2552,7 +2552,7 @@ function theme_user_filters($form) {
  * Process result from user administration filter form.
  */
 function user_filter_form_submit($form_id, $form_values) {
-  $op = $_POST['op'];
+  $op = $form_values['op'];
   $filters = user_filters();
   switch ($op) {
     case t('Filter'): case t('Refine'):