diff --git a/docs/CURRENT-STATE.md b/docs/CURRENT-STATE.md
index 00352adbc..75162a3dd 100644
--- a/docs/CURRENT-STATE.md
+++ b/docs/CURRENT-STATE.md
@@ -3092,7 +3092,10 @@ down | auth-failed` (plus the unchanged `missing-key`/`unsupported`) with
 >   outlasts its retries, the proxy pauses upstream calls for the `Retry-After`
 >   (60 seconds when none, at most 10 minutes). A request whose points are all
 >   cached, fresh or stale, is still served; a request with any uncached point
->   gets 502 and the page uses its geoid fallback for that chunk. Each request
+>   gets 502, whose `partial` lists the real heights it has (null for the rest)
+>   when it has any, and the page keeps those and uses its geoid fallback only
+>   for the points without one. The same holds when the upstream answers a
+>   point with a null height. Each request
 >   that was waiting on the upstream when the 429 came back logs one warning;
 >   requests refused during the pause do not log. Client geoid
 >   fallbacks wait 60 seconds before retrying and self-heal to Re:Earth on the
diff --git a/src/data/terrainHeights.test.mjs b/src/data/terrainHeights.test.mjs
index b39cf44e1..a3eaddf3d 100644
--- a/src/data/terrainHeights.test.mjs
+++ b/src/data/terrainHeights.test.mjs
@@ -19,6 +19,7 @@ import assert from 'node:assert/strict';
 import {
   resolveEllipsoidalGround,
   cachedEllipsoidalGround,
+  cachedRealEllipsoidalGround,
 } from './terrainHeights.js';
 
 const AUSTIN = { lat: 30.2672, lon: -97.7431 };
@@ -362,3 +363,47 @@ test('resolveEllipsoidalGround: null and string heights cannot become real zeroe
     );
   }
 });
+
+test('resolveEllipsoidalGround: a 502 keeps the real heights it carries and falls back only for the rest', async () => {
+  const coords = [
+    { lat: 62.001, lon: -150.001, sourceOrthometricM: 10 },
+    { lat: 62.002, lon: -150.002, sourceOrthometricM: 10 },
+    { lat: 62.003, lon: -150.003, sourceOrthometricM: 10 },
+  ];
+  await withFakeFetch(
+    async () => ({
+      ok: false,
+      status: 502,
+      json: async () => ({
+        error: 'terrain heights fetch failed and no cache available for every point',
+        partial: [{ ellipsoid: 412.5 }, null, { ellipsoid: 'x' }],
+      }),
+    }),
+    async () => {
+      const out = await resolveEllipsoidalGround(coords);
+      assert.deepEqual(out[0], { ellipsoid: 412.5, source: 'reearth' });
+      assert.equal(out[1].source, 'geoid-fallback');
+      assert.equal(out[2].source, 'geoid-fallback', 'a non-numeric height is not real');
+    }
+  );
+  assert.equal(cachedRealEllipsoidalGround(62.001, -150.001), 412.5);
+  assert.equal(cachedRealEllipsoidalGround(62.002, -150.002), null);
+});
+
+test('resolveEllipsoidalGround: a partial list of the wrong length is ignored', async () => {
+  const coords = [
+    { lat: 63.001, lon: -151.001 },
+    { lat: 63.002, lon: -151.002 },
+  ];
+  await withFakeFetch(
+    async () => ({
+      ok: false,
+      status: 502,
+      json: async () => ({ error: 'x', partial: [{ ellipsoid: 7 }] }),
+    }),
+    async () => {
+      const out = await resolveEllipsoidalGround(coords);
+      assert.deepEqual(out.map((r) => r.source), ['geoid-fallback', 'geoid-fallback']);
+    }
+  );
+});
diff --git a/src/data/terrainHeightsProxy.js b/src/data/terrainHeightsProxy.js
index f06ff3671..c17e595fb 100644
--- a/src/data/terrainHeightsProxy.js
+++ b/src/data/terrainHeightsProxy.js
@@ -190,7 +190,8 @@ export async function fetchTerrainChunkWithRetry(
  * Resolve a requested point batch against a per-point cache and a missing-only
  * fetcher. Results are reconstructed by canonical key in exact request order,
  * including duplicates. Stale values remain eligible only when refresh fails.
- * If any position has no real height, return 502 with no fabricated result.
+ * If any position has no real height, return 502 with no fabricated result;
+ * the body's `partial` lists the real heights it has, null for the rest.
  *
  * @param {object} options
  * @param {Array<[number, number]>} options.points
@@ -269,11 +270,19 @@ export async function resolveTerrainHeightRequest({
     return entry && validTerrainResult(entry.result) ? entry.result : null;
   });
   if (results.some((result) => result == null)) {
+    // The real heights this request does have, null elsewhere, so the page
+    // keeps them and uses its geoid only for the rest. Named `partial`, not
+    // `results`, so no reader mistakes it for a complete answer; left out when
+    // no point has a height.
+    const partial = results.some((result) => result != null)
+      ? { partial: results }
+      : {};
     return {
       status: 502,
       body: {
         error:
           'terrain heights fetch failed and no cache available for every point',
+        ...partial,
       },
       cacheChanged,
       upstreamError,
diff --git a/src/data/terrainHeightsProxy.test.mjs b/src/data/terrainHeightsProxy.test.mjs
index c9e143337..6e0b31332 100644
--- a/src/data/terrainHeightsProxy.test.mjs
+++ b/src/data/terrainHeightsProxy.test.mjs
@@ -268,3 +268,31 @@ test('terrain parser rejects out-of-range WGS84 points and accepts inclusive bou
     [0, 0],
   ]);
 });
+
+test('a 502 lists the real heights it has, null for the rest', async () => {
+  const cache = new Map([
+    [terrainPointKey([1, 1]), { at: 0, result: result('stale-a', 11) }],
+  ]);
+  const response = await resolveTerrainHeightRequest({
+    points: [
+      [1, 1],
+      [2, 2],
+      [1, 1],
+    ],
+    cache,
+    ttlMs: 100,
+    now: () => 1000,
+    fetchMissing: async () => {
+      const error = new Error('HTTP 429');
+      error.status = 429;
+      error.coolingDown = true;
+      throw error;
+    },
+  });
+  assert.equal(response.status, 502);
+  assert.equal('results' in response.body, false);
+  assert.deepEqual(
+    response.body.partial.map((item) => item?.id ?? null),
+    ['stale-a', null, 'stale-a'],
+  );
+});
diff --git a/src/services/requests.js b/src/services/requests.js
index 3e3a819eb..28f56265e 100644
--- a/src/services/requests.js
+++ b/src/services/requests.js
@@ -150,12 +150,25 @@ export function createApplicationRequestServices({
         const query = points
           .map(({ lat, lon }) => `${lon.toFixed(5)},${lat.toFixed(5)}`)
           .join(';');
-        return requireOk(
-          await request(`${urls.terrain}?points=${encodeURIComponent(query)}`, {
-            signal,
-          }),
-          'Terrain heights',
-        )?.results;
+        const response = await request(
+          `${urls.terrain}?points=${encodeURIComponent(query)}`,
+          { signal },
+        );
+        // A failed request still carries the real heights the server had, so
+        // the caller can keep them; null marks a point without one.
+        const partial = response.data?.partial;
+        if (
+          !response.ok &&
+          Array.isArray(partial) &&
+          partial.length === points.length
+        ) {
+          const error = new Error(
+            `Terrain heights unavailable (${response.status})`,
+          );
+          error.partial = partial;
+          throw error;
+        }
+        return requireOk(response, 'Terrain heights')?.results;
       },
     },
     regional: {
diff --git a/src/services/requests.test.mjs b/src/services/requests.test.mjs
index 2cbc464cd..ddfc378b0 100644
--- a/src/services/requests.test.mjs
+++ b/src/services/requests.test.mjs
@@ -94,3 +94,20 @@ test('a failed probe is retried after its backoff, not on every query', async ()
     'GET /api/overpass/status',
   ]);
 });
+
+test('a failed terrain request carries the real heights the server had', async () => {
+  const partial = [{ ellipsoid: 412.5 }, null];
+  const services = createApplicationRequestServices({
+    fetchImpl: async () => Response.json({ error: 'x', partial }, { status: 502 }),
+  });
+  const points = [{ lat: 30, lon: -97 }, { lat: 31, lon: -97 }];
+  await assert.rejects(services.terrain.getHeights(points), (error) => {
+    assert.match(error.message, /Terrain heights unavailable \(502\)/);
+    assert.deepEqual(error.partial, partial);
+    return true;
+  });
+  await assert.rejects(services.terrain.getHeights(points.slice(0, 1)), (error) => {
+    assert.equal(error.partial, undefined, 'a list of the wrong length is not attached');
+    return true;
+  });
+});
diff --git a/src/services/terrainHeights.js b/src/services/terrainHeights.js
index f84a4413f..00cddafe7 100644
--- a/src/services/terrainHeights.js
+++ b/src/services/terrainHeights.js
@@ -226,7 +226,8 @@ export function createTerrainHeights({
    * - Remaining (deduplicated) coordinates are sent to `/api/terrain/heights`
    *   in sequential chunks of <=64 points.
    * - If a chunk request fails (network error, non-ok HTTP, malformed body),
-   *   every point in THAT chunk falls back to geoid math
+   *   every point in THAT chunk without a real height in the failure's
+   *   `partial` falls back to geoid math
    *   (`sourceOrthometricM + geoidHeight` or `geoidHeight` alone) rather than
    *   failing the whole batch — a transient proxy outage in the middle of a
    *   large batch shouldn't blank out entities whose chunk happened to land
@@ -314,15 +315,34 @@ export function createTerrainHeights({
             cacheStore(item.key, entry);
           }
         }
-      } catch {
+      } catch (error) {
         requestSignal?.throwIfAborted();
         // Proxy down (or cold cache had nothing to serve-stale) — fall back to
-        // geoid math for every point in this chunk. `ensureGeoidReady()` is
-        // awaited lazily, only on the fallback path, so the common (proxy
-        // healthy) case never pays for the geoid grid's dynamic import.
+        // geoid math for the points in this chunk. A failure that still
+        // carries real heights (the proxy's `partial`, e.g. cached points
+        // during an upstream 429 pause) keeps them; only the rest use the
+        // geoid. `ensureGeoidReady()` is awaited lazily, only on the fallback
+        // path, so the common (proxy healthy) case never pays for the geoid
+        // grid's dynamic import.
+        const partial =
+          Array.isArray(error?.partial) && error.partial.length === chunk.length
+            ? error.partial
+            : [];
+        const fallback = [];
+        chunk.forEach((item, index) => {
+          const ellipsoid = partial[index]?.ellipsoid;
+          if (!Number.isFinite(ellipsoid)) {
+            fallback.push(item);
+            return;
+          }
+          const entry = { ellipsoid, source: 'reearth' };
+          resolvedThisCall.set(item.key, entry);
+          cacheStore(item.key, entry);
+        });
+        if (fallback.length === 0) continue;
         await ensureGeoidReady();
         requestSignal?.throwIfAborted();
-        for (const item of chunk) {
+        for (const item of fallback) {
           const ellipsoid = geoidFallback(
             item.lat,
             item.lon,