diff --git a/doc/api/crypto.md b/doc/api/crypto.md
index 696fe4fc4e7907..99623e92eccddb 100644
--- a/doc/api/crypto.md
+++ b/doc/api/crypto.md
@@ -735,8 +735,10 @@ module):
 added: v0.7.5
 -->
 
-The `DiffieHellmanGroup` class takes a well-known modp group as its argument but
-otherwise works the same as `DiffieHellman`.
+The `DiffieHellmanGroup` class takes a well-known modp group as its argument.
+It works the same as `DiffieHellman`, except that it does not allow changing
+its keys after creation. In other words, it does not implement `setPublicKey()`
+or `setPrivateKey()` methods.
 
 ```js
 const name = 'modp1';