diff --git a/docs/ref/contrib/gis/functions.txt b/docs/ref/contrib/gis/functions.txt
index b000f29d42..1d1aac6a2d 100644
--- a/docs/ref/contrib/gis/functions.txt
+++ b/docs/ref/contrib/gis/functions.txt
@@ -397,7 +397,9 @@ Accepts a single geographic field or expression and returns the memory size
 
 Accepts a single geographic field or expression and returns the number of
 geometries if the geometry field is a collection (e.g., a ``GEOMETRYCOLLECTION``
-or ``MULTI*`` field); otherwise returns ``None``.
+or ``MULTI*`` field). Returns 1 for single geometries.
+
+On MySQL, returns ``None`` for single geometries.
 
 ``NumPoints``
 =============