Index: src/wp-includes/media.php
===================================================================
--- src/wp-includes/media.php	(revision 32496)
+++ src/wp-includes/media.php	(working copy)
@@ -704,7 +704,7 @@
 	}
 	if ( $src && $width && $height )
 		return array( $src, $width, $height );
-	return false;
+	return apply_filters('wp_get_attachment_image_src_fallback', false, array($attachment_id, $size, $icon));
 }
 
 /**