diff --git a/modules/block/block.module b/modules/block/block.module
index 3a988de..dde26ea 100644
--- a/modules/block/block.module
+++ b/modules/block/block.module
@@ -880,9 +880,11 @@ function _block_render_blocks($region_blocks) {
       else {
         $array = module_invoke($block->module, 'block_view', $block->delta);
 
+        // Valid PHP function names cannot contain hyphens.
+        $delta = str_replace('-', '_', $block->delta);
         // Allow modules to modify the block before it is viewed, via either
         // hook_block_view_alter() or hook_block_view_MODULE_DELTA_alter().
-        drupal_alter(array('block_view', "block_view_{$block->module}_{$block->delta}"), $array, $block);
+        drupal_alter(array('block_view', "block_view_{$block->module}_{$delta}"), $array, $block);
 
         if (isset($cid)) {
           cache_set($cid, $array, 'cache_block', CACHE_TEMPORARY);
diff --git a/modules/block/block.test b/modules/block/block.test
index 11d0709..aad01f7 100644
--- a/modules/block/block.test
+++ b/modules/block/block.test
@@ -193,7 +193,7 @@ class BlockTestCase extends DrupalWebTestCase {
   }
 
   /**
-   * Test block visibility when using "pages" restriction but leaving 
+   * Test block visibility when using "pages" restriction but leaving
    * "pages" textarea empty
    */
   function testBlockVisibilityListedEmpty() {
@@ -753,6 +753,47 @@ class BlockTemplateSuggestionsUnitTest extends DrupalUnitTestCase {
 }
 
 /**
+ * Unit tests for hook_block_view_MODULE_DELTA_alter().
+ */
+class BlockViewModuleDeltaAlterWebTest extends DrupalWebTestCase {
+
+  public static function getInfo() {
+    return array(
+      'name' => 'Block view module delta alter',
+      'description' => 'Test the hook_block_view_MODULE_DELTA_alter() hook.',
+      'group' => 'Block',
+    );
+  }
+
+  public function setUp() {
+    parent::setUp(array('block_test'));
+  }
+
+  /**
+   * Test if hook_block_view_MODULE_DELTA_alter() is called, even if the delta
+   * contains a hyphen.
+   */
+  public function testBlockViewModuleDeltaAlter() {
+    $block = new stdClass;
+    $block->module = 'block_test';
+    $block->delta = 'test_underscore';
+    $block->title = '';
+    $render = array_pop(_block_render_blocks(array('region' => $block)));
+    $test_underscore = $render->content['#markup'];
+    $this->assertEqual($test_underscore, 'hook_block_view_MODULE_DELTA_alter', 'Found expected altered block content for delta with underscore');
+
+    $block = new stdClass;
+    $block->module = 'block_test';
+    $block->delta = 'test-hyphen';
+    $block->title = '';
+    $render = array_pop(_block_render_blocks(array('region' => $block)));
+    $test_hyphen = $render->content['#markup'];
+    $this->assertEqual($test_hyphen, 'hook_block_view_MODULE_DELTA_alter', 'Hyphens (-) in block delta were replaced by underscore (_)');
+  }
+
+}
+
+/**
  * Tests that hidden regions do not inherit blocks when a theme is enabled.
  */
 class BlockHiddenRegionTestCase extends DrupalWebTestCase {
diff --git a/modules/block/tests/block_test.module b/modules/block/tests/block_test.module
index 5e06d5c..475ebc8 100644
--- a/modules/block/tests/block_test.module
+++ b/modules/block/tests/block_test.module
@@ -22,6 +22,14 @@ function block_test_block_info() {
     'cache' => variable_get('block_test_caching', DRUPAL_CACHE_PER_ROLE),
   );
 
+  $blocks['test_underscore'] = array(
+    'info' => t('Test underscore'),
+  );
+
+  $blocks['test-hyphen'] = array(
+    'info' => t('Test hyphen'),
+  );
+
   $blocks['test_html_id'] = array(
     'info' => t('Test block html id'),
   );
@@ -34,3 +42,17 @@ function block_test_block_info() {
 function block_test_block_view($delta = 0) {
   return array('content' => variable_get('block_test_content', ''));
 }
+
+/**
+ * Implements hook_block_view_MODULE_DELTA_alter().
+ */
+function block_test_block_view_block_test_test_underscore_alter(&$data, $block) {
+  $data['content'] = 'hook_block_view_MODULE_DELTA_alter';
+}
+
+/**
+ * Implements hook_block_view_MODULE_DELTA_alter().
+ */
+function block_test_block_view_block_test_test_hyphen_alter(&$data, $block) {
+  $data['content'] = 'hook_block_view_MODULE_DELTA_alter';
+}