diff --git a/src/app/api/analytics/merchants/[merchant]/route.ts b/src/app/api/analytics/merchants/[merchant]/route.ts
index 28bb4d5..2361bd3 100644
--- a/src/app/api/analytics/merchants/[merchant]/route.ts
+++ b/src/app/api/analytics/merchants/[merchant]/route.ts
@@ -1,7 +1,7 @@
 import { NextRequest, NextResponse } from "next/server";
 import { getCurrentUser } from "@/lib/auth";
 import { queryRaw } from "@/lib/db";
-import { OWNER_SCOPE, STATEMENTS_JOIN } from "@/lib/analytics-sql";
+import { OWNER_SCOPE, STATEMENTS_JOIN, EFFECTIVE_CATEGORY } from "@/lib/analytics-sql";
 
 export async function GET(
   req: NextRequest,
@@ -38,7 +38,7 @@ export async function GET(
           (CASE WHEN ts.share_percent IS NOT NULL THEN COALESCE(t.amount_aud, t.amount) * ts.share_percent / 100 WHEN o.my_share_percent IS NOT NULL THEN COALESCE(t.amount_aud, t.amount) * o.my_share_percent / 100 ELSE COALESCE(t.amount_aud, t.amount) END)
       END::numeric(10,2) as my_amount,
       t.transaction_type,
-      COALESCE(o.category_override, t.category) as category,
+      ${EFFECTIVE_CATEGORY} as category,
       COALESCE(s.bank_name, 'Manual') as bank_name,
       t.statement_id
     FROM transactions t
diff --git a/src/app/api/analytics/merchants/route.ts b/src/app/api/analytics/merchants/route.ts
index 45799c5..23cdc41 100644
--- a/src/app/api/analytics/merchants/route.ts
+++ b/src/app/api/analytics/merchants/route.ts
@@ -1,7 +1,7 @@
 import { NextRequest, NextResponse } from "next/server";
 import { getCurrentUser } from "@/lib/auth";
 import { queryRaw } from "@/lib/db";
-import { OWNER_SCOPE, STATEMENTS_JOIN, EXCLUDE_NON_SPEND } from "@/lib/analytics-sql";
+import { OWNER_SCOPE, STATEMENTS_JOIN, EXCLUDE_NON_SPEND, EFFECTIVE_CATEGORY } from "@/lib/analytics-sql";
 
 // Split-adjusted amount helper (positive for spend, negative for refunds)
 const MY_AMOUNT = `CASE WHEN ts.share_percent IS NOT NULL THEN COALESCE(t.amount_aud, t.amount) * ts.share_percent / 100 WHEN o.my_share_percent IS NOT NULL THEN COALESCE(t.amount_aud, t.amount) * o.my_share_percent / 100 ELSE COALESCE(t.amount_aud, t.amount) END`;
@@ -39,7 +39,7 @@ export async function GET(req: NextRequest) {
   }>(`
     SELECT
       COALESCE(o.merchant_normalized, t.merchant_normalized, t.merchant_name, t.description) as merchant,
-      MODE() WITHIN GROUP (ORDER BY COALESCE(o.category_override, t.category)) as category,
+      MODE() WITHIN GROUP (ORDER BY ${EFFECTIVE_CATEGORY}) as category,
       COUNT(*) FILTER (WHERE t.transaction_type IN ('debit', 'fee', 'interest'))::int as debit_count,
       COUNT(*) FILTER (WHERE t.transaction_type IN ('refund', 'credit'))::int as refund_count,
       COALESCE(SUM(
diff --git a/src/lib/categories.ts b/src/lib/categories.ts
index 1178815..8a74989 100644
--- a/src/lib/categories.ts
+++ b/src/lib/categories.ts
@@ -36,7 +36,10 @@ export const CATEGORIES = [
 
 export type Category = (typeof CATEGORIES)[number];
 
-export function formatCategory(cat: string): string {
+// Tolerates null/undefined: an uncategorised transaction must never be able to
+// crash a page that renders its category.
+export function formatCategory(cat: string | null | undefined): string {
+  if (!cat) return "Uncategorised";
   return cat
     .split("_")
     .map((w) => w.charAt(0).toUpperCase() + w.slice(1))