diff --git a/src/logging/diagnostic-stability-bundle.test.ts b/src/logging/diagnostic-stability-bundle.test.ts
index 5b76aa00586..666076e7f73 100644
--- a/src/logging/diagnostic-stability-bundle.test.ts
+++ b/src/logging/diagnostic-stability-bundle.test.ts
@@ -268,6 +268,17 @@ describe("diagnostic stability bundles", () => {
         },
         error: "snapshot.events[0].seq",
       },
+      {
+        name: "out-of-range-event-timestamp",
+        bundle: {
+          ...baseBundle,
+          snapshot: {
+            ...baseBundle.snapshot,
+            events: [{ seq: 1, ts: 9e15, type: "webhook.received" }],
+          },
+        },
+        error: "snapshot.events[0].ts",
+      },
       {
         name: "null-summary",
         bundle: {
diff --git a/src/logging/diagnostic-stability-bundle.ts b/src/logging/diagnostic-stability-bundle.ts
index 281058a5f57..2d30f5f4a48 100644
--- a/src/logging/diagnostic-stability-bundle.ts
+++ b/src/logging/diagnostic-stability-bundle.ts
@@ -169,6 +169,14 @@ function readNumber(value: unknown, label: string): number {
   return value;
 }
 
+function readTimestampMs(value: unknown, label: string): number {
+  const timestamp = readNumber(value, label);
+  if (Number.isNaN(new Date(timestamp).getTime())) {
+    throw new Error(`Invalid stability bundle: ${label} must be a valid timestamp`);
+  }
+  return timestamp;
+}
+
 function readOptionalNumber(value: unknown, label: string): number | undefined {
   if (value === undefined) {
     return undefined;
@@ -197,7 +205,7 @@ function readStabilitySnapshot(value: unknown): DiagnosticStabilitySnapshot {
   for (const [index, event] of snapshot.events.entries()) {
     const record = readObject(event, `snapshot.events[${index}]`);
     readNumber(record.seq, `snapshot.events[${index}].seq`);
-    readNumber(record.ts, `snapshot.events[${index}].ts`);
+    readTimestampMs(record.ts, `snapshot.events[${index}].ts`);
     readString(record.type, `snapshot.events[${index}].type`);
   }
   const summary = readObject(snapshot.summary, "snapshot.summary");