diff --git a/include/openssl/ec.h b/include/openssl/ec.h
index f866ae9..dee41b7 100644
--- a/include/openssl/ec.h
+++ b/include/openssl/ec.h
@@ -302,7 +302,7 @@
 // EC_GROUP_set_generator sets the generator for |group| to |generator|, which
 // must have the given order and cofactor. It may only be used with |EC_GROUP|
 // objects returned by |EC_GROUP_new_curve_GFp| and may only be used once on
-// each group.
+// each group. |generator| must have been created using |group|.
 OPENSSL_EXPORT int EC_GROUP_set_generator(EC_GROUP *group,
                                           const EC_POINT *generator,
                                           const BIGNUM *order,