diff -u b/modules/demo/src/Tests/TMGMTDemoTest.php b/modules/demo/src/Tests/TMGMTDemoTest.php
--- b/modules/demo/src/Tests/TMGMTDemoTest.php
+++ b/modules/demo/src/Tests/TMGMTDemoTest.php
@@ -53,6 +53,10 @@
     // Check to see if no items are selected and the error message pops up.
     $this->drupalPostForm('admin/tmgmt/sources', array(), t('Request translation'));
     $this->assertUniqueText(t("You didn't select any source objects."));
+    $this->drupalPostForm('admin/tmgmt/sources', array(), t('Search'));
+    $this->assertNoText(t("You didn't select any source objects."));
+    $this->drupalPostForm('admin/tmgmt/sources', array(), t('Cancel'));
+    $this->assertNoText(t("You didn't select any source objects."));
   }
 
 }
diff -u b/src/Form/SourceOverviewForm.php b/src/Form/SourceOverviewForm.php
--- b/src/Form/SourceOverviewForm.php
+++ b/src/Form/SourceOverviewForm.php
@@ -155,10 +155,16 @@
   public function validateForm(array &$form, FormStateInterface $form_state) {
     $items = array_filter($form_state->getValue('items'));
     $is_search = FALSE;
-    if ($form_state->getValue('op') == t('Search')) {
+    $is_cancel = FALSE;
+    if ($form['search_wrapper']['search_submit']['#value'] == $form_state->getTriggeringElement()['#value']) {
       $is_search = TRUE;
     }
-    if (empty($items) && !$is_search) {
+    if (array_key_exists('search_cancel', $form['search_wrapper'])) {
+      if ($form['search_wrapper']['search_cancel']['#value'] == $form_state->getTriggeringElement()['#value']) {
+        $is_cancel = TRUE;
+      }
+    }
+    if (!$items && !$is_search && !$is_cancel) {
       $form_state->setError($form, t("You didn't select any source objects."));
     }
     $plugin = $form_state->get('plugin');