diff --git a/doc/manual/source/the-model-file.rst b/doc/manual/source/the-model-file.rst
index 8464b1ee8e2fecec11bc8e7651c7d417e2ece7d1..daa60ee8e9e804c2a02072999b47d055c09f3dc6 100644
--- a/doc/manual/source/the-model-file.rst
+++ b/doc/manual/source/the-model-file.rst
@@ -740,7 +740,9 @@ required for external functions used in an EXPRESSION outside of a
         provided as the only output of the M-/MEX file given as the
         option argument. If NAME is not provided, this tells Dynare
         that the M-/MEX file specified by the argument passed to NAME
-        returns the Jacobian as its second output argument.
+        returns the Jacobian as its second output argument. When this option is
+        not provided, Dynare will use finite difference approximations for
+        computing the derivatives of the function, whenever needed.
 
     .. option:: second_deriv_provided [= NAME]
 
@@ -750,7 +752,9 @@ required for external functions used in an EXPRESSION outside of a
         that the M-/MEX file specified by the argument passed to NAME
         returns the Hessian as its third output argument. NB: This
         option can only be used if the ``first_deriv_provided`` option
-        is used in the same ``external_function`` command.
+        is used in the same ``external_function`` command. When this option is
+        not provided, Dynare will use finite difference approximations for
+        computing the Hessian derivatives of the function, whenever needed.
 
     *Example*