diff --git a/CHANGELOG.md b/CHANGELOG.md
index 074c6f754..e2dc1ec2b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,8 @@ of current runtime behavior, see [`docs/CURRENT-STATE.md`](docs/CURRENT-STATE.md
 
 ### Fixed
 
+- FIRMS records a source as successful only after appending its rows, avoiding
+  contradictory success/failure status if aggregation throws.
 - Radio country filtering and voice country requests now resolve common English
   names and exonyms that `Intl.DisplayNames`' primary label omits, so requests
   like "play radio in Turkey" no longer fail closed (Turkey → Türkiye, plus
diff --git a/docs/CURRENT-STATE.md b/docs/CURRENT-STATE.md
index e85c38db0..b70fdf86a 100644
--- a/docs/CURRENT-STATE.md
+++ b/docs/CURRENT-STATE.md
@@ -10,6 +10,13 @@ Launch payloads with missing records now say PAYLOAD DATA UNAVAILABLE. Missing n
 
 Updated: August 24, 2026
 
+## FIRMS source status
+
+The FIRMS proxy records source success after appending its rows. If aggregation
+throws, that source reports failure without a contradictory success entry.
+The existing per-record append continues to support large feeds; sequential
+fetching, trailing-24-hour filtering and partial-success caching are unchanged.
+
 ## Installations and map-source guidance
 
 - On an uncached Overpass failure, mapped installations keep their existing
diff --git a/src/data/firmsProxy.test.mjs b/src/data/firmsProxy.test.mjs
new file mode 100644
index 000000000..5de363090
--- /dev/null
+++ b/src/data/firmsProxy.test.mjs
@@ -0,0 +1,80 @@
+import assert from 'node:assert/strict';
+import fs from 'node:fs';
+import test from 'node:test';
+import { filterTrailing24h, parseFirmsCsv } from './firmsCsv.js';
+
+const config = fs.readFileSync(new URL('../../vite.config.js', import.meta.url), 'utf8');
+const start = config.indexOf('  async function refreshUpstream(key) {');
+assert.notEqual(start, -1, 'FIRMS refresh function exists');
+const end = config.indexOf('\n  }', start);
+assert.notEqual(end, -1, 'FIRMS refresh function closes');
+const refreshSource = config.slice(start, end + 4);
+const SOURCES = ['VIIRS_NOAA20_NRT', 'VIIRS_NOAA21_NRT', 'VIIRS_SNPP_NRT'];
+const NOW = Date.UTC(2026, 8, 11, 12);
+const recent = { acqDate: '2026-09-11', acqTime: '1100' };
+
+// Exercise the production refresh without opening a server or using a MAP_KEY.
+// Inject only its upstream, clock and filter dependencies; keep its aggregation
+// and source-status code intact, including failures while consuming records.
+function createRefresh(fetchSource, filter = filterTrailing24h) {
+  return new Function('SOURCES', 'fetchSource', 'filterTrailing24h', 'Date', 'console',
+    `return (${refreshSource});`)(SOURCES, fetchSource, filter, { now: () => NOW }, { warn() {} });
+}
+
+test('FIRMS retains large sources in order and filters expired rows', async () => {
+  const header = 'latitude,longitude,acq_date,acq_time,confidence,frp\n';
+  const large = parseFirmsCsv(header + '1,2,2026-09-11,1100,n,4\n'.repeat(200_000));
+  const expired = { ...recent, acqDate: '2026-09-09' };
+  const last = { ...recent, marker: 'last' };
+  const calls = [];
+  let active = 0;
+  const refresh = createRefresh(async (key, source) => {
+    assert.equal(active++, 0, 'sources must be fetched sequentially');
+    calls.push(source);
+    await Promise.resolve();
+    active--;
+    return source === SOURCES[0] ? [...large, expired] : source === SOURCES[1] ? [last] : [];
+  });
+  const result = await refresh('fixture');
+  assert.deepEqual(calls, SOURCES);
+  assert.equal(result.fires.length, 200_001);
+  assert.equal(result.fires[0], large[0]);
+  assert.equal(result.fires[199_999], large.at(-1));
+  assert.equal(result.fires.at(-1), last);
+  assert.deepEqual(result.sources, SOURCES.map((source, index) => ({
+    source, count: [200_000, 1, 0][index], ok: true,
+  })));
+});
+
+test('FIRMS keeps successful sources when another upstream fails', async () => {
+  const result = await createRefresh(async (key, source) => {
+    if (source === SOURCES[1]) throw new Error('upstream unavailable');
+    return [recent];
+  })('fixture');
+  assert.equal(result.fires.length, 2);
+  assert.deepEqual(result.sources, SOURCES.map((source, index) => ({
+    source, count: index === 1 ? 0 : 1, ok: index !== 1,
+  })));
+});
+
+test('FIRMS reports one failure if consuming a source throws before append', async () => {
+  const failing = [];
+  const result = await createRefresh(async (key, source) => source === SOURCES[0] ? failing : [recent],
+    (records, now) => {
+      if (records !== failing) return filterTrailing24h(records, now);
+      // Fault injection for aggregation; ordinary parsed CSV returns an array.
+      return { length: 1, [Symbol.iterator]() { throw new Error('aggregation failed'); } };
+    })('fixture');
+  assert.equal(result.fires.length, 2);
+  assert.deepEqual(result.sources, SOURCES.map((source, index) => ({
+    source, count: index === 0 ? 0 : 1, ok: index !== 0,
+  })));
+});
+
+test('FIRMS distinguishes all-source failure from successful empty sources', async () => {
+  await assert.rejects(createRefresh(async () => { throw new Error('upstream unavailable'); })('fixture'),
+    /all FIRMS sources failed/);
+  const result = await createRefresh(async () => [])('fixture');
+  assert.deepEqual(result.fires, []);
+  assert.deepEqual(result.sources, SOURCES.map(source => ({ source, count: 0, ok: true })));
+});
diff --git a/vite.config.js b/vite.config.js
index 34dac5291..0ad4f2c37 100644
--- a/vite.config.js
+++ b/vite.config.js
@@ -2094,11 +2094,11 @@ function firmsProxy() {
     for (const source of SOURCES) {
       try {
         const records = filterTrailing24h(await fetchSource(key, source), now);
-        sources.push({ source, count: records.length, ok: true });
         // NOT fires.push(...records): spread passes each record as an argument,
         // and a world/2 VIIRS pull exceeds V8's argument limit (~125k) at
         // ~131k records — RangeError, and the whole source is silently dropped.
         for (const record of records) fires.push(record);
+        sources.push({ source, count: records.length, ok: true });
       } catch (err) {
         console.warn(`[firms-proxy] ${source} fetch failed:`, err?.message || err);
         sources.push({ source, count: 0, ok: false });