diff --git a/crypto/verificationhelper/sas.go b/crypto/verificationhelper/sas.go
index f5f13773..4cd1dd9e 100644
--- a/crypto/verificationhelper/sas.go
+++ b/crypto/verificationhelper/sas.go
@@ -157,7 +157,7 @@ func (vh *VerificationHelper) ConfirmSAS(ctx context.Context, txnID id.Verificat
 	if txn.ReceivedTheirMAC {
 		txn.VerificationState = VerificationStateSASMACExchanged
 
-		if err := vh.trustKeysAfterMACCheck(ctx, txn, masterKey); err != nil {
+		if err := vh.trustKeysAfterMACCheck(ctx, txn, txn.TheirMasterKey); err != nil {
 			return fmt.Errorf("failed to trust keys: %w", err)
 		}
 
@@ -750,6 +750,7 @@ func (vh *VerificationHelper) onVerificationMAC(ctx context.Context, txn Verific
 	log.Info().Msg("All MACs verified")
 
 	txn.ReceivedTheirMAC = true
+	txn.TheirMasterKey = masterKey
 	if txn.SentOurMAC {
 		txn.VerificationState = VerificationStateSASMACExchanged
 
diff --git a/crypto/verificationhelper/verificationhelper_sas_test.go b/crypto/verificationhelper/verificationhelper_sas_test.go
index 283eca84..60768fb9 100644
--- a/crypto/verificationhelper/verificationhelper_sas_test.go
+++ b/crypto/verificationhelper/verificationhelper_sas_test.go
@@ -358,3 +358,76 @@ func TestVerification_SAS_BothCallStart(t *testing.T) {
 	assert.True(t, sendingCallbacks.IsVerificationDone(txnID))
 	assert.True(t, receivingCallbacks.IsVerificationDone(txnID))
 }
+
+func TestCrossSignVerification_SAS(t *testing.T) {
+	ctx := log.Logger.WithContext(t.Context())
+
+	testCases := []struct {
+		sendingConfirmsFirst bool
+	}{
+		{true},
+		{false},
+	}
+
+	for _, tc := range testCases {
+		t.Run(fmt.Sprintf("sendingConfirmsFirst=%t", tc.sendingConfirmsFirst), func(t *testing.T) {
+			ts, sendingClient, receivingClient, _, _, sendingMachine, receivingMachine := initServerAndLoginAliceBob(t, ctx)
+			sendingCallbacks, receivingCallbacks, sendingHelper, receivingHelper := initDefaultCallbacks(t, ctx, sendingClient, receivingClient, sendingMachine, receivingMachine)
+			var err error
+
+			_, _, err = sendingMachine.GenerateAndUploadCrossSigningKeys(ctx, nil, "")
+			require.NoError(t, err)
+			_, _, err = receivingMachine.GenerateAndUploadCrossSigningKeys(ctx, nil, "")
+			require.NoError(t, err)
+
+			_, err = sendingMachine.FetchKeys(ctx, []id.UserID{bobUserID}, true)
+			require.NoError(t, err)
+			_, err = receivingMachine.FetchKeys(ctx, []id.UserID{aliceUserID}, true)
+			require.NoError(t, err)
+
+			txnID, err := sendingHelper.StartVerification(ctx, bobUserID)
+			require.NoError(t, err)
+			ts.DispatchToDevice(t, ctx, receivingClient)
+			err = receivingHelper.AcceptVerification(ctx, txnID)
+			require.NoError(t, err)
+			ts.DispatchToDevice(t, ctx, sendingClient)
+
+			err = sendingHelper.StartSAS(ctx, txnID)
+			require.NoError(t, err)
+
+			ts.DispatchToDevice(t, ctx, receivingClient)
+			ts.DispatchToDevice(t, ctx, sendingClient)
+			ts.DispatchToDevice(t, ctx, receivingClient)
+			ts.DispatchToDevice(t, ctx, sendingClient)
+
+			assert.Equal(t, sendingCallbacks.GetDecimalsShown(txnID), receivingCallbacks.GetDecimalsShown(txnID))
+
+			if tc.sendingConfirmsFirst {
+				err = sendingHelper.ConfirmSAS(ctx, txnID)
+				require.NoError(t, err)
+
+				ts.DispatchToDevice(t, ctx, receivingClient)
+
+				err = receivingHelper.ConfirmSAS(ctx, txnID)
+				require.NoError(t, err)
+
+				ts.DispatchToDevice(t, ctx, sendingClient)
+				ts.DispatchToDevice(t, ctx, receivingClient)
+			} else {
+				err = receivingHelper.ConfirmSAS(ctx, txnID)
+				require.NoError(t, err)
+
+				ts.DispatchToDevice(t, ctx, sendingClient)
+
+				err = sendingHelper.ConfirmSAS(ctx, txnID)
+				require.NoError(t, err)
+
+				ts.DispatchToDevice(t, ctx, receivingClient)
+				ts.DispatchToDevice(t, ctx, sendingClient)
+			}
+
+			assert.True(t, sendingCallbacks.IsVerificationDone(txnID))
+			assert.True(t, receivingCallbacks.IsVerificationDone(txnID))
+		})
+	}
+}
diff --git a/crypto/verificationhelper/verificationstore.go b/crypto/verificationhelper/verificationstore.go
index 1eb8f752..77679c1e 100644
--- a/crypto/verificationhelper/verificationstore.go
+++ b/crypto/verificationhelper/verificationstore.go
@@ -90,6 +90,7 @@ type VerificationTransaction struct {
 	EphemeralPublicKeyShared bool                                 `json:"ephemeral_public_key_shared,omitempty"` // Whether this device's ephemeral public key has been shared
 	OtherPublicKey           *ECDHPublicKey                       `json:"other_public_key,omitempty"`            // The other device's ephemeral public key
 	ReceivedTheirMAC         bool                                 `json:"received_their_mac,omitempty"`          // Whether we have received their MAC
+	TheirMasterKey           string                               `json:"their_master_key,omitempty"`            // The other user's master key from their MAC event
 	SentOurMAC               bool                                 `json:"sent_our_mac,omitempty"`                // Whether we have sent our MAC
 	ReceivedTheirDone        bool                                 `json:"received_their_done,omitempty"`         // Whether we have received their done event
 	SentOurDone              bool                                 `json:"sent_our_done,omitempty"`               // Whether we have sent our done event