diff --git a/backend/src/lib/audit-security.js b/backend/src/lib/audit-security.js
index 14602d37..d7268bae 100644
--- a/backend/src/lib/audit-security.js
+++ b/backend/src/lib/audit-security.js
@@ -36,6 +36,16 @@ function stableStringify(value, depth = 0, seen = new WeakSet()) {
   if (value === null || value === undefined) return "null";
   if (typeof value !== "object") return JSON.stringify(value);
 
+  // Date has no own enumerable properties, so the generic Object.entries()
+  // path below silently serializes any Date to "{}", discarding the actual
+  // timestamp. old_value/new_value in a profile-change audit event can be a
+  // Date (e.g. a timestamp field changing), so this must be special-cased
+  // before the object/array branches — otherwise the audit trail records a
+  // meaningless "{}" instead of the value that actually changed.
+  if (value instanceof Date) {
+    return JSON.stringify(value.toISOString());
+  }
+
   if (seen.has(value)) {
     return '"[Circular]"';
   }
diff --git a/backend/src/lib/audit-security.test.js b/backend/src/lib/audit-security.test.js
index 52234938..d188bccf 100644
--- a/backend/src/lib/audit-security.test.js
+++ b/backend/src/lib/audit-security.test.js
@@ -23,6 +23,21 @@ describe("audit-security", () => {
     expect(value).toBe('{"a":1,"b":2}');
   });
 
+  it("preserves the timestamp when sanitizing a Date value (#1331)", () => {
+    // Date has no own enumerable properties, so the generic object-serialization
+    // path used to silently collapse any Date into "{}", losing the actual
+    // value entirely — e.g. a profile-change audit event recording a
+    // timestamp field change.
+    const date = new Date("2026-01-01T12:00:00.000Z");
+    expect(sanitizeAuditValue(date)).toBe('"2026-01-01T12:00:00.000Z"');
+  });
+
+  it("produces different hashes for payloads that differ only by Date value (#1331)", () => {
+    const before = hashAuditPayload({ old_value: new Date("2026-01-01T00:00:00.000Z") });
+    const after = hashAuditPayload({ old_value: new Date("2026-06-01T00:00:00.000Z") });
+    expect(before).not.toBe(after);
+  });
+
   it("redacts sensitive audit field names", () => {
     expect(sanitizeAuditKey("api_key")).toBe("[REDACTED]");
     expect(sanitizeAuditKey("notification_email")).toBe("notification_email");