diff --git a/auth/request.go b/auth/request.go
index 8f39fc9db835f30e41e51e6a6fe5db377aef666f..78cd2160680d240cac61917de0867a79dc3f419c 100644
--- a/auth/request.go
+++ b/auth/request.go
@@ -137,6 +137,11 @@ func requestAuth(partner, me contact.Contact, rng io.Reader, reset bool,
 	sender := storage.GetUser().ReceptionID
 
 	//generate ownership proof
+	if !dhGrp.Inside(partner.DhPubKey.GetLargeInt()) {
+		return 0, errors.Errorf("partner's DH public key is not in the E2E "+
+			"group; E2E group fingerprint is %d and DH key has %d",
+			dhGrp.GetFingerprint(), partner.DhPubKey.GetGroupFingerprint())
+	}
 	ownership := cAuth.MakeOwnershipProof(originDHPrivKey, partner.DhPubKey,
 		dhGrp)
 	confirmFp := cAuth.MakeOwnershipProofFP(ownership)