diff --git a/docs/scaled-unit-class.rst b/docs/scaled-unit-class.rst
index 42725e00..ec32844c 100644
--- a/docs/scaled-unit-class.rst
+++ b/docs/scaled-unit-class.rst
@@ -30,7 +30,7 @@ Context
 Introduction
 ------------
 
-.. code-block::cpp
+.. code-block:: cpp
 
     #include <xo/unit/scaled_unit.hpp>