diff --git a/src/GeoJson/CoordinateReferenceSystem/CoordinateReferenceSystem.php b/src/GeoJson/CoordinateReferenceSystem/CoordinateReferenceSystem.php
index 3fe1633..2633c91 100644
--- a/src/GeoJson/CoordinateReferenceSystem/CoordinateReferenceSystem.php
+++ b/src/GeoJson/CoordinateReferenceSystem/CoordinateReferenceSystem.php
@@ -17,6 +17,10 @@
 /**
  * Coordinate reference system object.
  *
+ * @deprecated 1.1 Specification of coordinate reference systems has been removed, i.e.,
+ *                 the 'crs' member of [GJ2008] is no longer used.
+ *
+ * @see https://www.rfc-editor.org/rfc/rfc7946#appendix-B.1
  * @see http://www.geojson.org/geojson-spec.html#coordinate-reference-system-objects
  * @since 1.0
  */
diff --git a/src/GeoJson/CoordinateReferenceSystem/Linked.php b/src/GeoJson/CoordinateReferenceSystem/Linked.php
index 9a5ecf9..8fa130e 100644
--- a/src/GeoJson/CoordinateReferenceSystem/Linked.php
+++ b/src/GeoJson/CoordinateReferenceSystem/Linked.php
@@ -13,6 +13,10 @@
 /**
  * Linked coordinate reference system object.
  *
+ * @deprecated 1.1 Specification of coordinate reference systems has been removed, i.e.,
+ *                 the 'crs' member of [GJ2008] is no longer used.
+ *
+ * @see https://www.rfc-editor.org/rfc/rfc7946#appendix-B.1
  * @see http://www.geojson.org/geojson-spec.html#linked-crs
  * @since 1.0
  */
diff --git a/src/GeoJson/CoordinateReferenceSystem/Named.php b/src/GeoJson/CoordinateReferenceSystem/Named.php
index ef4fb48..2c40a66 100644
--- a/src/GeoJson/CoordinateReferenceSystem/Named.php
+++ b/src/GeoJson/CoordinateReferenceSystem/Named.php
@@ -13,6 +13,9 @@
 /**
  * Named coordinate reference system object.
  *
+ * @deprecated 1.1 Specification of coordinate reference systems has been removed, i.e.,
+ *                 the 'crs' member of [GJ2008] is no longer used.
+ *
  * @see http://www.geojson.org/geojson-spec.html#named-crs
  * @since 1.0
  */