diff --git a/modules/block/block.module b/modules/block/block.module
index 7790600..9d119f1 100644
--- a/modules/block/block.module
+++ b/modules/block/block.module
@@ -943,7 +943,7 @@ function template_preprocess_block(&$variables) {
 
   $variables['theme_hook_suggestions'][] = 'block__' . $variables['block']->region;
   $variables['theme_hook_suggestions'][] = 'block__' . $variables['block']->module;
-  $variables['theme_hook_suggestions'][] = 'block__' . $variables['block']->module . '__' . $variables['block']->delta;
+  $variables['theme_hook_suggestions'][] = 'block__' . $variables['block']->module . '__' . strtr($variables['block']->delta, '-', '_');
 
   // Create a valid HTML ID and make sure it is unique.
   $variables['block_html_id'] = drupal_html_id('block-' . $variables['block']->module . '-' . $variables['block']->delta);