diff --git a/src/libstrongswan/crypto/proposal/proposal.c b/src/libstrongswan/crypto/proposal/proposal.c
index ff7884d9a..b8c74906e 100644
--- a/src/libstrongswan/crypto/proposal/proposal.c
+++ b/src/libstrongswan/crypto/proposal/proposal.c
@@ -324,7 +324,8 @@ static bool select_algo(private_proposal_t *this, proposal_t *other,
 
 	if (is_ke_transform(type))
 	{
-		optional = this->protocol == PROTO_ESP || this->protocol == PROTO_AH;
+		optional = this->protocol == PROTO_ESP || this->protocol == PROTO_AH ||
+				   type != KEY_EXCHANGE_METHOD;
 	}
 
 	e1 = create_enumerator(this, type);