--- openid_provider.inc
+++ openid_provider.inc
@@ -142,6 +142,9 @@ function openid_provider_authentication_response($request) {
     return openid_redirect_http($response['openid.return_to'], $response); 
   }
   else {
+    // Unset global post variable, otherwise FAPI will assume it has been 
+    // submitted against openid_provider_form.
+    unset($_POST);
     return drupal_get_form('openid_provider_form', $response, $realm);
   }
 }
--- openid_provider.module
+++ openid_provider.module
@@ -200,7 +200,7 @@ function openid_provider_xrds($account = NULL) {
 function openid_provider_form(&$form_state, &$response = array(), $realm = NULL) {
   global $user;
 
-  // Use form_state to store the $response and $realm values 
+  // Use form_state to store the $response and $realm values.
   if (count($response)) {
     $form_state['storage']['response'] = $response;
   }
@@ -216,14 +216,14 @@ function openid_provider_form(&$form_state, &$response = array(), $realm = NULL)
   }
   
   $form = array();
-  
+  // Force FAPI to cache this form so that $form_state['storage'] is available 
+  // in submit handler.
+  $form['#cache'] = TRUE;
+  $form['#action'] = url('openid/provider/send');
   $form['intro'] = array(
     '#type' => 'markup',
     '#value' => '<p>'. t('You are being logged into %site, would you like to continue?', array('%site' => $realm)) . '</p>'
   );
-  
-  $form['#action'] = url('openid/provider/send');
-
   $form['submit_once'] = array(
     '#type' => 'submit',
     '#value' => t('Yes; just this once'),