diff --git a/src/lib/inbox-three/save-lines.test.ts b/src/lib/inbox-three/save-lines.test.ts
index a37c988..b2a1a3e 100644
--- a/src/lib/inbox-three/save-lines.test.ts
+++ b/src/lib/inbox-three/save-lines.test.ts
@@ -5,6 +5,8 @@ import type { LineEdit } from "./line-rows";
 
 const MESH_ITEM = "meshitem1234567";
 const BAILING_ITEM = "bailingitem12345";
+/** An order line the slip sells in metres. */
+const KERB_ITEM = "kerbitem12345678";
 /** An order line from another purchase order. */
 const FOREIGN_ITEM = "foreignitem12345";
 
@@ -15,6 +17,7 @@ const context = (): PreviewContext => ({
   po: { id: "poabcdefghijklm", purchase_order_number: "MEGCPO9448", total_value: 11748.7 },
   poItems: [
     { id: MESH_ITEM, description: "MESH DIAMOND 600 x 2.5 ROLL", unit: "m", qty: 2, rate: 1124.35, disc_percent: 0, vat_percent: 15 },
+    { id: KERB_ITEM, description: "KERB 150", unit: "m", qty: 100, rate: 150, disc_percent: 0, vat_percent: 15 },
     { id: BAILING_ITEM, description: "1.6mm Bailing Wire", unit: "ea", qty: 100, rate: 95, disc_percent: 0, vat_percent: 15 },
   ],
   lines: [
@@ -85,8 +88,25 @@ describe("saveLineEdits", () => {
     expect(rules.some((rule) => rule.receiving_match?.factor === 30)).toBe(true);
   });
 
-  it("saves nothing when one edit in the batch fails", () => {
+  it("keeps a combined line even when the supplier rule cannot be remembered", () => {
     const c = context();
+    // Two kerb lines on one order line, sold in metres: there is no single
+    // product to scope a supplier rule to, so the rule is skipped — but the
+    // edit itself has to stand.
+    const result = saveLineEdits(c, preview(c), [edit({
+      lines: [1, 2],
+      poItemId: KERB_ITEM,
+      slipQty: 4,
+      slipUnit: "ea",
+      factor: 15,
+      reason: "One kerb is 15 m.",
+    })], "operator");
+    expect(result.remembered).toBeNull();
+    expect(result.preview.allocations.some((allocation) =>
+      allocation.purchaseOrderItemId === KERB_ITEM && allocation.sourceLineIds.length === 2)).toBe(true);
+  });
+
+  it("saves nothing when one edit in the batch fails", () => {    const c = context();
     const before = preview(c);
     const untouched = structuredClone(before);
     expect(() => saveLineEdits(c, before, [
diff --git a/src/lib/inbox-three/save-lines.ts b/src/lib/inbox-three/save-lines.ts
index 643fedd..db0de6a 100644
--- a/src/lib/inbox-three/save-lines.ts
+++ b/src/lib/inbox-three/save-lines.ts
@@ -101,15 +101,23 @@ export function saveLineEdits(
     const item = edit.poItemId ? working.poItems.find((candidate) => candidate.id === edit.poItemId) : null;
     const targetUnit = item && typeof item.unit === "string" ? item.unit : null;
     if (targetUnit && edit.factor !== null && edit.factor !== 1 && edit.slipUnit.trim().toLowerCase() !== targetUnit.trim().toLowerCase()) {
-      const guidance = rememberConnection(
-        { ...working, supplier: { ...working.supplier, reconciliation_rules: remembered ?? working.supplier.reconciliation_rules } },
-        current,
-        current.allocations.findIndex((allocation) => sameLines(allocation.sourceLineIds, sourceLineIds)),
-        actor,
-      );
-      remembered = guidance;
-      working = { ...working, supplier: { ...working.supplier, reconciliation_rules: guidance } };
-      current = { ...current, snapshotHash: snapshotHash(working) };
+      try {
+        const guidance = rememberConnection(
+          { ...working, supplier: { ...working.supplier, reconciliation_rules: remembered ?? working.supplier.reconciliation_rules } },
+          current,
+          current.allocations.findIndex((allocation) => sameLines(allocation.sourceLineIds, sourceLineIds)),
+          actor,
+        );
+        remembered = guidance;
+        working = { ...working, supplier: { ...working.supplier, reconciliation_rules: guidance } };
+        current = { ...current, snapshotHash: snapshotHash(working) };
+      } catch (error) {
+        // A rule that cannot be written must not lose the edit: a combined
+        // line has no single product to scope the rule to. The line still
+        // books and the office still sees it — the supplier rule is simply
+        // not remembered this time.
+        if (!(error instanceof Error) || !/can be remembered/i.test(error.message)) throw error;
+      }
     }
   }