diff --git a/doc/tags/block.rst b/doc/tags/block.rst
index e38048232..0fb60c635 100644
--- a/doc/tags/block.rst
+++ b/doc/tags/block.rst
@@ -5,7 +5,6 @@ Blocks are used for inheritance and act as placeholders and replacements at
 the same time. They are documented in detail in the documentation for the
 :doc:`extends<../tags/extends>` tag.
 
-Block names should consist of alphanumeric characters, and underscores. Dashes
-are not permitted.
+Block names must consist of alphanumeric characters, and underscores. The first char can't be a digit and dashes are not permitted.
 
 .. seealso:: :doc:`block<../functions/block>`, :doc:`parent<../functions/parent>`, :doc:`use<../tags/use>`, :doc:`extends<../tags/extends>`