diff --git a/routing/mock_test.go b/routing/mock_test.go
index cf828baf..0d0b7a5b 100644
--- a/routing/mock_test.go
+++ b/routing/mock_test.go
@@ -333,6 +333,10 @@ func (m *mockControlTower) RegisterAttempt(phash lntypes.Hash,
 		return channeldb.ErrPaymentAlreadyFailed
 	}
 
+	if settled || failed {
+		return channeldb.ErrPaymentTerminal
+	}
+
 	// Add attempt to payment.
 	p.attempts = append(p.attempts, channeldb.HTLCAttempt{
 		HTLCAttemptInfo: *a,
diff --git a/routing/payment_lifecycle_test.go b/routing/payment_lifecycle_test.go
index e8aa8c51..01383d21 100644
--- a/routing/payment_lifecycle_test.go
+++ b/routing/payment_lifecycle_test.go
@@ -650,6 +650,56 @@ func TestRouterPaymentStateMachine(t *testing.T) {
 			},
 			paymentErr: channeldb.ErrPaymentAlreadyFailed,
 		},
+		{
+			// A MP payment scenario when our path finding returns
+			// after we've just received a terminal failure, and
+			// we have another shard still in flight.
+			name: "MP shard in flight after terminal",
+
+			steps: []string{
+				routerInitPayment,
+
+				// shard 0
+				routeRelease,
+				routerRegisterAttempt,
+				sendToSwitchSuccess,
+
+				// shard 1
+				routeRelease,
+				routerRegisterAttempt,
+				sendToSwitchSuccess,
+
+				// shard 2
+				routeRelease,
+				routerRegisterAttempt,
+				sendToSwitchSuccess,
+
+				// We find a path for another shard.
+				routeRelease,
+
+				// shard 0 fails with a terminal error.
+				getPaymentResultTerminalFailure,
+				routerFailAttempt,
+				routerFailPayment,
+
+				// We try to register our final shard after
+				// processing a terminal failure.
+				routerRegisterAttempt,
+
+				// Our in-flight shards fail.
+				getPaymentResultTempFailure,
+				getPaymentResultTempFailure,
+				routerFailAttempt,
+				routerFailAttempt,
+
+				// Payment fails.
+				paymentError,
+			},
+			routes: []*route.Route{
+				shard, shard, shard, shard,
+			},
+			paymentErr: channeldb.ErrPaymentTerminal,
+		},
 	}
 
 	for _, test := range tests {