diff --git a/api.md b/api.md
index 3c016a2..a2e285b 100644
--- a/api.md
+++ b/api.md
@@ -18,7 +18,8 @@ The map-to-G2 function if `mode = MCL_MAP_TO_MODE_ETH2`.
 void mclBn_setOriginalG2cofactor(int enable);
 ```
 Use faster multiplication of `G2` with cofactor if `enable = 1`.
-This is disabled if `mclBn_setMapToMode(MCL_MAP_TO_MODE_ETH2)`.
+This is enabled if `mclBn_setMapToMode(MCL_MAP_TO_MODE_ETH2)`.
+if `enable = 0`, then [the fast algorithm (mulByCofactorBLS12)](https://github.com/herumi/mcl/blob/master/include/mcl/bn.hpp#L463) is used.
 
 ## Minimum sample