diff --git a/src/shielding/middleware/handle-invalid-query-string-values.js b/src/shielding/middleware/handle-invalid-query-string-values.js
index 142069d4cbd0..fadc45ee90e2 100644
--- a/src/shielding/middleware/handle-invalid-query-string-values.js
+++ b/src/shielding/middleware/handle-invalid-query-string-values.js
@@ -32,7 +32,7 @@ const RECOGNIZED_VALUES_KEYS = new Set(Object.keys(RECOGNIZED_VALUES))
 export default function handleInvalidQuerystringValues(req, res, next) {
   const { method, query } = req
   if (method === 'GET' || method === 'HEAD') {
-    for (const key of Object.keys(query)) {
+    for (const [key, value] of Object.entries(query)) {
       if (RECOGNIZED_VALUES_KEYS.has(key)) {
         const validValues = RECOGNIZED_VALUES[key]
         const values = Array.isArray(query[key]) ? query[key] : [query[key]]
@@ -66,6 +66,17 @@ export default function handleInvalidQuerystringValues(req, res, next) {
           return
         }
       }
+
+      // For example ?foo[bar]=baz (but not ?foo=bar&foo=baz)
+      if (value instanceof Object && !Array.isArray(value)) {
+        const message = `Invalid query string key (${key})`
+        defaultCacheControl(res)
+        res.status(400).send(message)
+
+        const tags = ['response:400', `path:${req.path}`, `key:${key}`]
+        statsd.increment(STATSD_KEY, 1, tags)
+        return
+      }
     }
   }
 
diff --git a/src/shielding/tests/invalid-querystrings.js b/src/shielding/tests/invalid-querystrings.js
index cdf9b95667ac..59fb7dac2cc1 100644
--- a/src/shielding/tests/invalid-querystrings.js
+++ b/src/shielding/tests/invalid-querystrings.js
@@ -57,11 +57,18 @@ describe('invalid query strings', () => {
     }
   })
 
+  test('query string keys with single square brackets', async () => {
+    const url = `/en?query[foo]=bar`
+    const res = await get(url)
+    expect(res.statusCode).toBe(400)
+    expect(res.body).toMatch('Invalid query string key (query)')
+  })
+
   test('query string keys with square brackets', async () => {
     const url = `/?constructor[foo][bar]=buz`
     const res = await get(url)
-    expect(res.statusCode).toBe(302)
-    expect(res.headers.location).toBe('/en')
+    expect(res.statusCode).toBe(400)
+    expect(res.body).toMatch('Invalid query string key (constructor)')
   })
 
   test('bad tool query string with Chinese URL-encoded characters', async () => {