diff --git a/apps/api/src/routes/admin.ts b/apps/api/src/routes/admin.ts
index 3f62d77..1ffd207 100644
--- a/apps/api/src/routes/admin.ts
+++ b/apps/api/src/routes/admin.ts
@@ -11,12 +11,13 @@
  *   - No console.log of request bodies or passwords in any handler (T-10-10).
  *
  * Routes:
- *   GET  /api/admin/members                    → list members + credential status (UI-SPEC Surface 2)
- *   POST /api/admin/members                    → create local member: users row + local_credentials (AUTH-LOCAL-07)
- *   POST /api/admin/members/:id/password       → admin reset local member password (AUTH-LOCAL-08)
- *   POST /api/admin/credentials                → validate+encrypt+store for any member (ADMIN-01)
- *   GET  /api/admin/calendars                  → list synced calendars (UI-SPEC Surface 5)
- *   PUT  /api/admin/calendars/:id/shared       → exclusive is_shared designation (ADMIN-02)
+ *   GET   /api/admin/members                    → list members + credential status + isAdmin (UI-SPEC Surface 2)
+ *   POST  /api/admin/members                    → create local member: users row + local_credentials (AUTH-LOCAL-07)
+ *   PATCH /api/admin/members/:id               → update member profile: displayName and/or isAdmin (Plan 20-01)
+ *   POST  /api/admin/members/:id/password       → admin reset local member password (AUTH-LOCAL-08)
+ *   POST  /api/admin/credentials                → validate+encrypt+store for any member (ADMIN-01)
+ *   GET   /api/admin/calendars                  → list synced calendars (UI-SPEC Surface 5)
+ *   PUT   /api/admin/calendars/:id/shared       → exclusive is_shared designation (ADMIN-02)
  *
  * Mounted in index.ts: app.route('/api/admin', adminRouter)
  */
@@ -105,6 +106,7 @@ adminRouter.get('/members', async (c) => {
       id: users.id,
       displayName: users.displayName,
       color: users.color,
+      isAdmin: users.isAdmin, // Plan 20-01: feeds editor admin toggle initial state (D-02)
       credentialId: memberCredentials.id,
       localCredId: localCredentials.id, // LEFT JOIN — null when no local_credentials row
     })
@@ -116,6 +118,7 @@ adminRouter.get('/members', async (c) => {
     id: row.id,
     displayName: row.displayName,
     color: row.color,
+    isAdmin: row.isAdmin, // Plan 20-01
     hasCredential: row.credentialId !== null,
     hasLocalCredential: row.localCredId !== null, // AUTH-LOCAL-17
   }));
@@ -208,6 +211,74 @@ adminRouter.post('/members', zValidator('json', createMemberSchema, noEchoHook),
   }
 });
 
+// ---------------------------------------------------------------------------
+// PATCH /api/admin/members/:id
+//
+// Updates a member's displayName and/or isAdmin flag (Plan 20-01, D-02, D-03).
+// Security:
+//   - requireAdmin: inherited from adminRouter.use('*', requireAdmin) (D-02 — no second guard)
+//   - noEchoHook: applied for consistency with other admin write routes (T-20-04)
+//   - D-03 last-admin guard: rejects isAdmin=false when target is the sole remaining admin (T-20-02)
+//   - parsePositiveIntParam: rejects malformed ids (T-20-03)
+// ---------------------------------------------------------------------------
+
+const updateMemberSchema = z.object({
+  displayName: z.string().min(1).max(256).optional(),
+  isAdmin: z.boolean().optional(),
+});
+
+adminRouter.patch(
+  '/members/:id',
+  zValidator('json', updateMemberSchema, noEchoHook),
+  async (c) => {
+    const targetId = parsePositiveIntParam(c.req.param('id'));
+    if (targetId === null) {
+      return c.json({ error: 'Invalid member id' }, 400);
+    }
+
+    const { displayName, isAdmin } = c.req.valid('json');
+    // T-20-04: NEVER log request body
+
+    // Verify the target user exists (404 if not)
+    const [target] = await db
+      .select({ id: users.id, isAdmin: users.isAdmin })
+      .from(users)
+      .where(eq(users.id, targetId))
+      .limit(1);
+
+    if (!target) {
+      return c.json({ error: 'Member not found' }, 404);
+    }
+
+    // D-03 last-admin guard: reject demotion of the only remaining admin (T-20-02)
+    if (isAdmin === false && target.isAdmin) {
+      const [{ count }] = await db
+        .select({ count: sql<number>`COUNT(*)` })
+        .from(users)
+        .where(eq(users.isAdmin, true));
+      if (Number(count) <= 1) {
+        return c.json({ error: 'Cannot remove the last admin' }, 409);
+      }
+    }
+
+    // Build a partial set() from whichever fields are present
+    const updates: { displayName?: string; isAdmin?: boolean } = {};
+    if (displayName !== undefined) updates.displayName = displayName;
+    if (isAdmin !== undefined) updates.isAdmin = isAdmin;
+
+    try {
+      await db.update(users).set(updates).where(eq(users.id, targetId));
+      return c.json({ ok: true }, 200);
+    } catch (err) {
+      console.error(
+        '[admin/PATCH /members/:id] Unexpected error:',
+        err instanceof Error ? err.message : String(err),
+      );
+      return c.json({ error: 'Service unavailable' }, 503);
+    }
+  },
+);
+
 // ---------------------------------------------------------------------------
 // POST /api/admin/members/:id/password
 //
diff --git a/apps/api/tests/routes/admin.test.ts b/apps/api/tests/routes/admin.test.ts
index 9bd1062..54012de 100644
--- a/apps/api/tests/routes/admin.test.ts
+++ b/apps/api/tests/routes/admin.test.ts
@@ -1151,6 +1151,7 @@ describe('PATCH /api/admin/members/:id', () => {
   it('Test D (self-demotion allowed): with two admins, PATCH { isAdmin: false } returns 200; one admin remains', async () => {
     const adminId1 = await seedUser('admin-demote-1', true);
     const adminId2 = await seedUser('admin-demote-2', true);
+    // Log in as adminId1 to perform the self-demotion
     currentDevUserId = adminId1;
     const app = await getApp();
 
@@ -1159,7 +1160,9 @@ describe('PATCH /api/admin/members/:id', () => {
     );
     expect(res.status).toBe(200);
 
-    // Only adminId2 should remain as admin
+    // Switch to adminId2 to verify the outcome — adminId1 is now non-admin
+    // and can no longer call GET /members (would 403).
+    currentDevUserId = adminId2;
     const getRes = await app.fetch(jsonRequest('GET', '/api/admin/members'));
     expect(getRes.status).toBe(200);
     const getBody = (await getRes.json()) as {