diff --git a/modules/block/block.module b/modules/block/block.module
index d0f07e447ba5a531a1fe592985d00e61df089043..920090f82241876f8e274be1392bc611a424f8a0 100644
--- a/modules/block/block.module
+++ b/modules/block/block.module
@@ -850,7 +850,7 @@ function _block_get_renderable_block($element) {
     // hook_block_view_alter() or hook_block_view_MODULE_DELTA_alter().
     drupal_alter(array('block_view', "block_view_{$block->module}_{$block->delta}"), $array, $block);
 
-    if (empty($array)) {
+    if (empty($array['content'])) {
       // Blocks without content should emit no markup at all.
       $element += array(
         '#access' => FALSE,
diff --git a/modules/block/block.test b/modules/block/block.test
index a6ab2bf3fe8ccb8ac755c26adf677f48b8e75178..0b41be52ef39614afd25797be6a38052cf0dba91 100644
--- a/modules/block/block.test
+++ b/modules/block/block.test
@@ -190,6 +190,9 @@ class BlockTestCase extends DrupalWebTestCase {
     $this->drupalLogout();
     $this->drupalGet('');
     $this->assertNoText($title, t('Block was not displayed to anonymous users.'));
+
+    // Confirm that an empty block is not displayed.
+    $this->assertNoRaw('block-system-help', t('Empty block not displayed.'));
   }
 
   /**
diff --git a/modules/book/book.module b/modules/book/book.module
index 6e74d3297efcaec7c45eb510d63543c9460e43d0..779c90704eed4e3de8303d43bffd52ed3169eb02 100644
--- a/modules/book/book.module
+++ b/modules/book/book.module
@@ -274,8 +274,9 @@ function book_block_view($delta = '') {
         $book_menus[$book_id] = menu_tree_output($pseudo_tree);
       }
     }
-    $book_menus['#theme'] = 'book_all_books_block';
-    $block['content'] = $book_menus;
+    if ($block['content'] = $book_menus) {
+      $book_menus['#theme'] = 'book_all_books_block';
+    }
   }
   elseif ($current_bid) {
     // Only display this block when the user is browsing a book.