diff --git a/services/o11y/src/alerting/gastown-health-query.ts b/services/o11y/src/alerting/gastown-health-query.ts
index cc1a7f071e..2823efaa38 100644
--- a/services/o11y/src/alerting/gastown-health-query.ts
+++ b/services/o11y/src/alerting/gastown-health-query.ts
@@ -16,12 +16,17 @@ type QueryEnv = {
 
 type FetchFn = (url: string, init?: RequestInit) => Promise<Response>;
 
+const AnalyticsEngineNumberSchema = z.preprocess(
+  value => (typeof value === 'string' && value.trim() !== '' ? Number(value) : value),
+  z.number().finite().nonnegative().nullable()
+);
+
 const GastownHealthResponseSchema = z.object({
   data: z.array(
     z.object({
       town_id: z.string(),
-      weighted_failed_checks: z.number().nonnegative().nullable(),
-      weighted_successful_checks: z.number().nonnegative().nullable(),
+      weighted_failed_checks: AnalyticsEngineNumberSchema,
+      weighted_successful_checks: AnalyticsEngineNumberSchema,
       latest_event_timestamp: z.string().nullable(),
     })
   ),
diff --git a/services/o11y/test/gastown-health-query.spec.ts b/services/o11y/test/gastown-health-query.spec.ts
index e4c968c20d..fc8bb660a6 100644
--- a/services/o11y/test/gastown-health-query.spec.ts
+++ b/services/o11y/test/gastown-health-query.spec.ts
@@ -31,20 +31,20 @@ describe('queryGastownHealth', () => {
         data: [
           {
             town_id: 'town-1',
-            weighted_failed_checks: 20,
-            weighted_successful_checks: 100,
+            weighted_failed_checks: '20',
+            weighted_successful_checks: '100',
             latest_event_timestamp: '2026-06-24 15:09:00.000',
           },
           {
             town_id: 'town-2',
-            weighted_failed_checks: 4,
-            weighted_successful_checks: 50,
+            weighted_failed_checks: '4',
+            weighted_successful_checks: '50',
             latest_event_timestamp: '2026-06-24 15:10:00.000',
           },
           {
             town_id: '',
-            weighted_failed_checks: 3,
-            weighted_successful_checks: 2,
+            weighted_failed_checks: '3',
+            weighted_successful_checks: '2',
             latest_event_timestamp: '2026-06-24 15:08:00.000',
           },
         ],
@@ -107,6 +107,25 @@ describe('queryGastownHealth', () => {
     });
   });
 
+  it.each(['', 'not-a-number', '-1', 'Infinity'])(
+    'rejects invalid Analytics Engine aggregate %j',
+    async aggregate => {
+      const fetchFn: FetchFn = async () =>
+        Response.json({
+          data: [
+            {
+              town_id: '',
+              weighted_failed_checks: aggregate,
+              weighted_successful_checks: '0',
+              latest_event_timestamp: null,
+            },
+          ],
+        });
+
+      await expect(queryGastownHealth(makeEnv(), fetchFn)).rejects.toThrow();
+    }
+  );
+
   it('rejects malformed Analytics Engine responses', async () => {
     const fetchFn: FetchFn = async () =>
       Response.json({ data: [{ weighted_failed_checks: '20' }] });