diff --git a/docs/ref/contrib/gis/functions.txt b/docs/ref/contrib/gis/functions.txt
index 164043d569..f2be78d45c 100644
--- a/docs/ref/contrib/gis/functions.txt
+++ b/docs/ref/contrib/gis/functions.txt
@@ -261,13 +261,16 @@ right-hand rule.
 ``GeoHash``
 ===========
 
-.. class:: GeoHash(expression, **extra)
+.. class:: GeoHash(expression, precision=None, **extra)
 
 *Availability*: PostGIS, SpatiaLite (LWGEOM)
 
 Accepts a single geographic field or expression and returns a `GeoHash`__
 representation of the geometry.
 
+The ``precision`` keyword argument controls the number of characters in the
+result.
+
 .. versionchanged:: 1.10
 
     SpatiaLite support was added.