diff --git a/FeedsOAIHTTPFetcher.inc b/FeedsOAIHTTPFetcher.inc
index 2679e61..3a329ee 100755
--- a/FeedsOAIHTTPFetcher.inc
+++ b/FeedsOAIHTTPFetcher.inc
@@ -197,7 +197,6 @@ class FeedsOAIHTTPFetcher extends FeedsHTTPFetcher {
    */
   public function sourceForm($source_config) {
     $form = parent::sourceForm($source_config);
-    $error = FALSE;
 
     // If earliest_timestamp is not set, and source is, then get info from
     // repository to populate settings.
@@ -210,15 +209,9 @@ class FeedsOAIHTTPFetcher extends FeedsHTTPFetcher {
       }
       else {
         drupal_set_message(t('There was a problem fetching repository information: !list', array('!list' => $result['output'])));
-        $error = TRUE;
       }
     }
 
-    if (isset($result) && $error == FALSE) {
-      // Build options array for sets available in repository.
-      $sets_options = feeds_oai_pmh_sets_options($result['repository']['sets']);
-    }
-
     // Override the default "source" element provided by Feeds.
     // Clearer label and description.
     $form['source']['#title'] = t('URL of OAI-PMH endpoint');
@@ -240,27 +233,17 @@ class FeedsOAIHTTPFetcher extends FeedsHTTPFetcher {
       if ($result['status'] == 0) {
         $source_config = array_merge($source_config, $result['repository']);
       }
-      elseif (isset($result['repository'])) {
-        $sets_options = feeds_oai_pmh_sets_options($result['repository']['sets']);
-      }
-      else {
-        $sets_options = feeds_oai_pmh_sets_options(array());
-      }
     }
 
+    // The set options are always created by the #process callback,
+    // feeds_oai_pmh_process_set_options(), even when the form is refreshed via
+    // AJAX.
     $form['set'] = array(
       '#type' => 'select',
       '#title' => t('Set to fetch'),
       '#default_value' => isset($source_config['set']) ? $source_config['set'] : NULL,
-      '#options' => isset($sets_options) ? $sets_options : array(),
-      '#suffix' => '',
-      '#ajax' => array(
-        'callback' => 'feeds_oai_pmh_ajax_callback',
-        'wrapper' => 'ahah-element',  // ID of div element to update.
-        'method' => 'replace',
-        'effect' => 'fade',
-        'event' => 'change',
-      ),
+      '#options' => array(),
+      '#process' => array('feeds_oai_pmh_process_set_options'),
     );
 
     if (isset($source_config['source']) && isset($source_config['set'])) {
diff --git a/feeds_oai_pmh.module b/feeds_oai_pmh.module
index 7459bdc..7c4934c 100755
--- a/feeds_oai_pmh.module
+++ b/feeds_oai_pmh.module
@@ -1,4 +1,5 @@
 <?php
+require_once(drupal_get_path('module', 'feeds_oai_pmh') . '/feeds_oai_pmh.inc');
 
 /**
  * Implementation of hook_feed_plugins().
@@ -30,6 +31,33 @@ function feeds_oai_pmh_feeds_plugins() {
 }
 
 /**
+ * Fills the set options array based on the source field value.
+ */
+function feeds_oai_pmh_process_set_options($element, $form_state, $form) {
+  $current_source_url = $form_state['values']['feeds']['FeedsOAIHTTPFetcher']['source'];
+  $default_source_url = $form_state['complete form']['feeds']['FeedsOAIHTTPFetcher']['source']['#default_value'];
+
+  // Check for the source URL in the $form_state['values'] array.
+  if (!empty($current_source_url)) {
+    // Get the repository information, which includes a list of sets.
+    $result = feeds_oai_pmh_identify($form_state['values']['feeds']['FeedsOAIHTTPFetcher']['source']);
+    if ($result['status'] == 0) {
+      // The OAI-PMH Identify verb returned OK.  Create the set options.
+      $element['#options'] = feeds_oai_pmh_sets_options($result['repository']['sets']);
+    }
+  }
+
+  // Check to see if the source field value has changed.
+  if ($current_source_url != $default_source_url) {
+    // Clear the set element's values to prevent validation errors.
+    unset($element['#default_value']);
+    unset($element['#value']);
+  }
+
+  return $element;
+}
+
+/**
  * Return a "drupalized" hierarchic options form element for the sets in a repository.
  */
 function feeds_oai_pmh_sets_options($sets) {
@@ -50,21 +78,13 @@ function feeds_oai_pmh_sets_options($sets) {
  * Callback function for AJAX setSpec element in form.
  */
 function feeds_oai_pmh_ajax_callback($form, $form_state) {
-  require_once(drupal_get_path('module', 'feeds_oai_pmh') . '/feeds_oai_pmh.inc');
-
   // Validate the repository.
   $oai_source_url = $form_state['values']['feeds']['FeedsOAIHTTPFetcher']['source'];
-  
+
   $result = feeds_oai_pmh_identify($oai_source_url);
 
   if ($result['status'] == 0) {
     // OAI-PMH Identify verb returned OK.
-    // Change the form's set element.
-    $form['feeds']['FeedsOAIHTTPFetcher']['set']['#options'] = feeds_oai_pmh_sets_options($result['repository']['sets']);
-    $set = $form_state['values']['feeds']['FeedsOAIHTTPFetcher']['set'];
-    if ($set) {
-      $form['feeds']['FeedsOAIHTTPFetcher']['set']['#default_value'] = $set;
-    }
     if (isset($result['repository']['earliest_timestamp']) && $result['repository']['earliest_timestamp'] > 0) {
       $date = format_date((int)$result['repository']['earliest_timestamp'], 'custom', 'M d, Y');
       $form['feeds']['FeedsOAIHTTPFetcher']['dates']['#description'] = t('Note: earliest record reported by repository is @date',
@@ -72,8 +92,6 @@ function feeds_oai_pmh_ajax_callback($form, $form_state) {
     }
   }
   else {
-    // Empty sets.
-    $form['feeds']['FeedsOAIHTTPFetcher']['set']['#options'] = feeds_oai_pmh_sets_options(array());
     $form['feeds']['FeedsOAIHTTPFetcher']['dates']['#description'] = '';
     drupal_set_message($result['output'], 'error');
   }