diff --git a/channeldb/invoice_test.go b/channeldb/invoice_test.go
index 45d072b5..4e01f52e 100644
--- a/channeldb/invoice_test.go
+++ b/channeldb/invoice_test.go
@@ -1216,6 +1216,94 @@ func TestInvoiceRef(t *testing.T) {
 	require.Equal(t, &payAddr, refByHashAndAddr.PayAddr())
 }
 
+// TestHTLCSet asserts that HTLCSet returns the proper set of accepted HTLCs
+// that can be considered for settlement. It asserts that MPP and AMP HTLCs do
+// not comingle, and also that HTLCs with disjoint set ids appear in different
+// sets.
+func TestHTLCSet(t *testing.T) {
+	inv := &Invoice{
+		Htlcs: make(map[CircuitKey]*InvoiceHTLC),
+	}
+
+	// Construct two distinct set id's, in this test we'll also track the
+	// nil set id as a third group.
+	setID1 := &[32]byte{1}
+	setID2 := &[32]byte{2}
+
+	// Create the expected htlc sets for each group, these will be updated
+	// as the invoice is modified.
+	expSetNil := make(map[CircuitKey]*InvoiceHTLC)
+	expSet1 := make(map[CircuitKey]*InvoiceHTLC)
+	expSet2 := make(map[CircuitKey]*InvoiceHTLC)
+
+	checkHTLCSets := func() {
+		require.Equal(t, expSetNil, inv.HTLCSet(nil))
+		require.Equal(t, expSet1, inv.HTLCSet(setID1))
+		require.Equal(t, expSet2, inv.HTLCSet(setID2))
+	}
+
+	// All HTLC sets should be empty initially.
+	checkHTLCSets()
+
+	// Add the following sequence of HTLCs to the invoice, sanity checking
+	// all three HTLC sets after each transition. This sequence asserts:
+	//   - both nil and non-nil set ids can have multiple htlcs.
+	//   - there may be distinct htlc sets with non-nil set ids.
+	//   - only accepted htlcs are returned as part of the set.
+	htlcs := []struct {
+		setID *[32]byte
+		state HtlcState
+	}{
+		{nil, HtlcStateAccepted},
+		{nil, HtlcStateAccepted},
+		{setID1, HtlcStateAccepted},
+		{setID1, HtlcStateAccepted},
+		{setID2, HtlcStateAccepted},
+		{setID2, HtlcStateAccepted},
+		{nil, HtlcStateCanceled},
+		{setID1, HtlcStateCanceled},
+		{setID2, HtlcStateCanceled},
+		{nil, HtlcStateSettled},
+		{setID1, HtlcStateSettled},
+		{setID2, HtlcStateSettled},
+	}
+
+	for i, h := range htlcs {
+		var ampData *InvoiceHtlcAMPData
+		if h.setID != nil {
+			ampData = &InvoiceHtlcAMPData{
+				Record: *record.NewAMP([32]byte{0}, *h.setID, 0),
+			}
+
+		}
+
+		// Add the HTLC to the invoice's set of HTLCs.
+		key := CircuitKey{HtlcID: uint64(i)}
+		htlc := &InvoiceHTLC{
+			AMP:   ampData,
+			State: h.state,
+		}
+		inv.Htlcs[key] = htlc
+
+		// Update our expected htlc set if the htlc is accepted,
+		// otherwise it shouldn't be reflected.
+		if h.state == HtlcStateAccepted {
+			switch h.setID {
+			case nil:
+				expSetNil[key] = htlc
+			case setID1:
+				expSet1[key] = htlc
+			case setID2:
+				expSet2[key] = htlc
+			default:
+				t.Fatalf("unexpected set id")
+			}
+		}
+
+		checkHTLCSets()
+	}
+}
+
 // TestDeleteInvoices tests that deleting a list of invoices will succeed
 // if all delete references are valid, or will fail otherwise.
 func TestDeleteInvoices(t *testing.T) {
diff --git a/channeldb/invoices.go b/channeldb/invoices.go
index cd8ffc83..bcff0629 100644
--- a/channeldb/invoices.go
+++ b/channeldb/invoices.go
@@ -362,6 +362,30 @@ type Invoice struct {
 	HodlInvoice bool
 }
 
+// HTLCSet returns the set of accepted HTLCs belonging to an invoice. Passing a
+// nil setID will return all accepted HTLCs in the case of legacy or MPP, and no
+// HTLCs in the case of AMP.  Otherwise, the returned set will be filtered by
+// the populated setID which is used to retrieve AMP HTLC sets.
+func (i *Invoice) HTLCSet(setID *[32]byte) map[CircuitKey]*InvoiceHTLC {
+	htlcSet := make(map[CircuitKey]*InvoiceHTLC)
+	for key, htlc := range i.Htlcs {
+		// Only consider accepted mpp htlcs. It is possible that there
+		// are htlcs registered in the invoice database that previously
+		// timed out and are in the canceled state now.
+		if htlc.State != HtlcStateAccepted {
+			continue
+		}
+
+		if !htlc.IsInHTLCSet(setID) {
+			continue
+		}
+
+		htlcSet[key] = htlc
+	}
+
+	return htlcSet
+}
+
 // HtlcState defines the states an htlc paying to an invoice can be in.
 type HtlcState uint8
 
@@ -420,6 +444,26 @@ type InvoiceHTLC struct {
 	AMP *InvoiceHtlcAMPData
 }
 
+// IsInHTLCSet returns true if this HTLC is part an HTLC set. If nil is passed,
+// this method returns true if this is an MPP HTLC. Otherwise, it only returns
+// true if the AMP HTLC's set id matches the populated setID.
+func (h *InvoiceHTLC) IsInHTLCSet(setID *[32]byte) bool {
+	wantAMPSet := setID != nil
+	isAMPHtlc := h.AMP != nil
+
+	// Non-AMP HTLCs cannot be part of AMP HTLC sets, and vice versa.
+	if wantAMPSet != isAMPHtlc {
+		return false
+	}
+
+	// Skip AMP HTLCs that have differing set ids.
+	if isAMPHtlc && *setID != h.AMP.Record.SetID() {
+		return false
+	}
+
+	return true
+}
+
 // InvoiceHtlcAMPData is a struct hodling the additional metadata stored for
 // each received AMP HTLC. This includes the AMP onion record, in addition to
 // the HTLC's payment hash and preimage.
diff --git a/invoices/update.go b/invoices/update.go
index f7eaf4e4..41bd690b 100644
--- a/invoices/update.go
+++ b/invoices/update.go
@@ -143,14 +143,7 @@ func updateMpp(ctx *invoiceUpdateCtx,
 
 	// Check whether total amt matches other htlcs in the set.
 	var newSetTotal lnwire.MilliSatoshi
-	for _, htlc := range inv.Htlcs {
-		// Only consider accepted mpp htlcs. It is possible that there
-		// are htlcs registered in the invoice database that previously
-		// timed out and are in the canceled state now.
-		if htlc.State != channeldb.HtlcStateAccepted {
-			continue
-		}
-
+	for _, htlc := range inv.HTLCSet(nil) {
 		if ctx.mpp.TotalMsat() != htlc.MppTotalAmt {
 			return nil, ctx.failRes(ResultHtlcSetTotalMismatch), nil
 		}
@@ -250,10 +243,8 @@ func updateLegacy(ctx *invoiceUpdateCtx,
 	// Don't allow settling the invoice with an old style
 	// htlc if we are already in the process of gathering an
 	// mpp set.
-	for _, htlc := range inv.Htlcs {
-		if htlc.State == channeldb.HtlcStateAccepted &&
-			htlc.MppTotalAmt > 0 {
-
+	for _, htlc := range inv.HTLCSet(nil) {
+		if htlc.MppTotalAmt > 0 {
 			return nil, ctx.failRes(ResultMppInProgress), nil
 		}
 	}