diff --git a/doc/RTD/source/Cooling/index.rst b/doc/RTD/source/Cooling/index.rst
index 46a01b2a054629b7fc13f0ea190c2a5a0fdd6d9c..585a5bd0e3cee8f0c6b55f3cc0878213b4882dc5 100644
--- a/doc/RTD/source/Cooling/index.rst
+++ b/doc/RTD/source/Cooling/index.rst
@@ -45,6 +45,9 @@ to provide an HDF5 table computed by Cloudy.
 When starting a simulation without providing the different fractions, the code
 supposes an equilibrium and computes the fractions automatically.
 
+In order to compile SWIFT with Grackle, you need to provide the options ``with-grackle``
+and ``with-chemistry``.
+
 Eagle
 ~~~~~