diff --git a/docs/source/format/Columnar.rst b/docs/source/format/Columnar.rst
index 9ef6a933528f8..e1603e8d8e3f6 100644
--- a/docs/source/format/Columnar.rst
+++ b/docs/source/format/Columnar.rst
@@ -693,7 +693,7 @@ having logical values::
 
 It may have the following representation: ::
 
-    * Length: 4, Null count: 1
+    * Length: 5, Null count: 1
     * Validity bitmap buffer:
 
       | Byte 0 (validity bitmap) | Bytes 1-63            |