diff --git a/hardware_interface/doc/hardware_interface_types_userdoc.rst b/hardware_interface/doc/hardware_interface_types_userdoc.rst
index 54b20035687..cd1e475b209 100644
--- a/hardware_interface/doc/hardware_interface_types_userdoc.rst
+++ b/hardware_interface/doc/hardware_interface_types_userdoc.rst
@@ -85,7 +85,9 @@ They can be combined together within the different hardware component types (sys
-
+
+ 3.1
+
diff --git a/hardware_interface/doc/mock_components_userdoc.rst b/hardware_interface/doc/mock_components_userdoc.rst
index 326b3dfd2a3..312d789712e 100644
--- a/hardware_interface/doc/mock_components_userdoc.rst
+++ b/hardware_interface/doc/mock_components_userdoc.rst
@@ -58,3 +58,19 @@ mimic (optional; string)
multiplier (optional; double; default: 1; used if mimic joint is defined)
Multiplier of values for mimicking joint defined in ``mimic`` parameter. Example: ``-2``.
+
+Per-interface Parameters
+,,,,,,,,,,,,,,,,,,,,,,,,
+
+initial_value (optional; double)
+ Initial value of certain state interface directly after startup. Example:
+
+ .. code-block:: xml
+
+
+ 3.45
+
+
+ Note: This parameter is shared with the gazebo and gazebo classic plugins for
+ joint interfaces. For Mock components it is also possible to set initial
+ values for gpio or sensor state interfaces.