diff --git a/src/Form/BreakpointFormTrait.php b/src/Form/BreakpointFormTrait.php
index 4b0bbfc..631da76 100644
--- a/src/Form/BreakpointFormTrait.php
+++ b/src/Form/BreakpointFormTrait.php
@@ -22,14 +22,22 @@ public static function breakpointFormValidate(array $element, FormStateInterface
       $form_state->setError($element['browser_size'], t('The browser size cannot be empty if ad size(s) exists.'));
     }
     elseif (!empty($element['browser_size']['#value']) && empty($element['ad_sizes']['#value'])) {
-      $form_state->setError($element['ad_sizes'], t('The ad size(s) cannot be empty if a browser size exists.'));
+      $form_state->setError($element['ad_sizes'], t(
+          'The ad size(s) cannot be empty if a browser size exists. If you wish to suppress an ad slot for a given browser size, you can enter "@none" in the ad size(s) field.',
+          array('@none' => '<none>')
+        )
+      );
     }
     if (!empty($element['browser_size']['#value']) && !empty($element['ad_sizes']['#value'])) {
       if (preg_match('/[^x|0-9]/', $element['browser_size']['#value'])) {
         $form_state->setError($element['browser_size'], t('The browser size can only contain numbers and the character x.'));
       }
-      elseif (preg_match('/[^x|,|0-9]/', $element['ad_sizes']['#value'])) {
-        $form_state->setError($element['ad_sizes'], t('The ad size(s) can only contain numbers, the character x and commas.'));
+      elseif ($element['ad_sizes']['#value'] != '<none>' && preg_match('/[^x|,|0-9]/', $element['ad_sizes']['#value'])) {
+        $form_state->setError($element['ad_sizes'], t(
+            'The ad size(s) string can only contain numbers, the character x and commas (unless it is the special keyword "@none").',
+            array('@none' => '<none>')
+          )
+        );
       }
     }
   }
@@ -158,7 +166,10 @@ protected function addBreakpointForm(array &$form, $key, array $data = []) {
     ];
     if (empty($data)) {
       $form['breakpoints']['table'][$key]['browser_size']['#description'] = $this->t('Example: 1024x768');
-      $form['breakpoints']['table'][$key]['ad_sizes']['#description'] = $this->t('Example: 300x600,300x250');
+      $form['breakpoints']['table'][$key]['ad_sizes']['#description'] = $this->t(
+        'Example: 300x600, 300x250. Enter "@none" to suppress this slot for a given browser size.',
+        array('@none' => '<none>')
+      );
     }
   }
 
diff --git a/src/Tests/DisplayTagTest.php b/src/Tests/DisplayTagTest.php
index 261359f..9d4ff33 100644
--- a/src/Tests/DisplayTagTest.php
+++ b/src/Tests/DisplayTagTest.php
@@ -69,7 +69,14 @@ public function testDisplayTagWithMapping() {
     $edit['breakpoints[0][browser_size]'] = $this->dfpGenerateSize();
     $edit['breakpoints[0][ad_sizes]'] = '100y100,200x200';
     $this->dfpEditTag($tag->id(), $edit);
-    $this->assertText(t('The ad size(s) can only contain numbers, the character x and commas.'), 'An error was correctly thrown when invalid characters.');
+    $this->assertText(t('The ad size(s) string can only contain numbers, the character x and commas (unless it is the special keyword "&lt;none&gt;").'), 'An error was correctly thrown when invalid characters.');
+
+    // Test tags with ad_size set to <none>.
+    $edit['breakpoints[0][browser_size]'] = '0x0';
+    $edit['breakpoints[0][ad_sizes]'] = '<none>';
+    $this->dfpEditTag($tag->id(), $edit);
+    $this->drupalGet('');
+    $this->assertRaw('addSize([0, 0], [])');
   }
 
   /**
diff --git a/src/View/TagView.php b/src/View/TagView.php
index 9b4cc10..b8ccd42 100644
--- a/src/View/TagView.php
+++ b/src/View/TagView.php
@@ -329,8 +329,15 @@ public static function formatSize($size) {
 
     $sizes = explode(',', $size);
     foreach ($sizes as $size) {
-      $formatted_size = explode('x', trim($size));
-      $formatted_sizes[] = '[' . implode(', ', $formatted_size) . ']';
+      if ($size == '<none>') {
+        // If the ad sizes string contains the special keyword "<none>," use an
+        // empty size list in order to suppress slot display.
+        $formatted_sizes[] = '[]';
+      }
+      else {
+        $formatted_size = explode('x', trim($size));
+        $formatted_sizes[] = '[' . implode(', ', $formatted_size) . ']';
+      }
     }
 
     return count($formatted_sizes) == 1 ? $formatted_sizes[0] : '[' . implode(', ', $formatted_sizes) . ']';
diff --git a/tests/src/Unit/View/TagViewTest.php b/tests/src/Unit/View/TagViewTest.php
index 95f644f..9d402d5 100644
--- a/tests/src/Unit/View/TagViewTest.php
+++ b/tests/src/Unit/View/TagViewTest.php
@@ -32,6 +32,7 @@ public function testFormatSize($size, $expected) {
    */
   public function formatSizeProvider() {
     return [
+      ['<none>', '[]'],
       ['300x250 ', '[300, 250]'],
       ['300x250, 728x90 ', '[[300, 250], [728, 90]]'],
     ];