diff --git a/docs/source_docs/user_guide/inputs/model_options.rst b/docs/source_docs/user_guide/inputs/model_options.rst
index 01c0e89955c0134a759581a9e68d14e1a70a03ad..293e6966270a096172e2d8731dce10747403dfc7 100644
--- a/docs/source_docs/user_guide/inputs/model_options.rst
+++ b/docs/source_docs/user_guide/inputs/model_options.rst
@@ -7,7 +7,7 @@ The following inputs are defined using the prefix ``mfix``:
 +------------------------+----------------------------------------------------------------------------+----------+---------------------+
 |                        | Description                                                                |   Type   | Default             |
 +========================+============================================================================+==========+=====================+
-| gravity                | Gravity vector.                                                            | Reals<3> | 0 0 0               |
+| gravity                | Gravity vector [required].                                                 | Reals<3> | 0 0 0               |
 +------------------------+----------------------------------------------------------------------------+----------+---------------------+
 | advect_density         | Enable time evolution of fluid density.                                    | Int      | 0                   |
 +------------------------+----------------------------------------------------------------------------+----------+---------------------+