diff --git a/doc/sphinx/cti/reactions.rst b/doc/sphinx/cti/reactions.rst
index 085340937..83d32d0a7 100644
--- a/doc/sphinx/cti/reactions.rst
+++ b/doc/sphinx/cti/reactions.rst
@@ -187,7 +187,8 @@ collision efficiency can be absorbed into the rate coefficient :math:`k_f(T)`, t
 default collision efficiency is 1.0.
 
 A three-body reaction may be defined using the :class:`three_body_reaction` entry. The equation string for a three-body
-reaction must contain an ``'M'`` or ``'m'`` on both the reactant and product sides of the equation.
+reaction must contain an ``'M'`` or ``'m'`` on both the reactant and product sides of the equation. The collision
+efficiencies are specified as a string, with the species name followed by a colon and the efficiency.
 
 Some examples from GRI-Mech 3.0 are shown below::