diff --git a/pages/api/address/balance/[address].ts b/pages/api/address/balance/[address].ts
index 93801e956..c0b79af29 100644
--- a/pages/api/address/balance/[address].ts
+++ b/pages/api/address/balance/[address].ts
@@ -6,7 +6,7 @@ import { runMiddleware, satoshisToUnit } from 'utils/index'
 import xecaddr from 'xecaddrjs'
 import { multiBlockchainClient } from 'services/chronikService'
 
-const { ADDRESS_NOT_PROVIDED_400 } = RESPONSE_MESSAGES
+const { ADDRESS_NOT_PROVIDED_400, INVALID_ADDRESS_400 } = RESPONSE_MESSAGES
 const cors = Cors({
   methods: ['GET', 'HEAD']
 })
@@ -24,6 +24,9 @@ export default async (req: NextApiRequest, res: NextApiResponse): Promise<void>
         case ADDRESS_NOT_PROVIDED_400.message:
           res.status(ADDRESS_NOT_PROVIDED_400.statusCode).json(ADDRESS_NOT_PROVIDED_400)
           break
+        case INVALID_ADDRESS_400.message:
+          res.status(INVALID_ADDRESS_400.statusCode).json(INVALID_ADDRESS_400)
+          break
         default:
           res.status(500).json({ statusCode: 500, message: err.message })
       }
diff --git a/pages/api/address/transactions/count/[address].ts b/pages/api/address/transactions/count/[address].ts
index e7bd9a62e..a2a70bebc 100644
--- a/pages/api/address/transactions/count/[address].ts
+++ b/pages/api/address/transactions/count/[address].ts
@@ -20,6 +20,9 @@ export default async (req: NextApiRequest, res: NextApiResponse): Promise<void>
         case RESPONSE_MESSAGES.MULTIPLE_USER_IDS_PROVIDED_400.message:
           res.status(400).json(RESPONSE_MESSAGES.MULTIPLE_USER_IDS_PROVIDED_400)
           break
+        case RESPONSE_MESSAGES.INVALID_ADDRESS_400.message:
+          res.status(RESPONSE_MESSAGES.INVALID_ADDRESS_400.statusCode).json(RESPONSE_MESSAGES.INVALID_ADDRESS_400)
+          break
         default:
           res.status(500).json({ statusCode: 500, message: err.message })
       }
diff --git a/tests/integration-tests/api.test.ts b/tests/integration-tests/api.test.ts
index 2fca22012..ca3592289 100644
--- a/tests/integration-tests/api.test.ts
+++ b/tests/integration-tests/api.test.ts
@@ -8,6 +8,7 @@ import walletsEndpoint from 'pages/api/wallets/index'
 import walletEndpoint from 'pages/api/wallet/index'
 import walletIdEndpoint from 'pages/api/wallet/[id]'
 import transactionsEndpoint from 'pages/api/address/transactions/[address]'
+import transactionCountEndpoint from 'pages/api/address/transactions/count/[address]'
 import balanceEndpoint from 'pages/api/address/balance/[address]'
 import dashboardEndpoint from 'pages/api/dashboard/index'
 import paymentsEndpoint from 'pages/api/payments/index'
@@ -1285,6 +1286,24 @@ describe('GET /api/address/transactions/[address]', () => {
   })
 })
 
+describe('GET /api/address/transactions/count/[address]', () => {
+  it('HTTP 400 when multiple address query parameters are provided', async () => {
+    const requestOptions: RequestOptions = {
+      method: 'GET' as RequestMethod,
+      headers: {
+        'Content-Type': 'application/json'
+      },
+      query: {
+        address: ['address1', 'address2']
+      }
+    }
+    const res = await testEndpoint(requestOptions, transactionCountEndpoint)
+    const responseData = res._getJSONData()
+    expect(res.statusCode).toBe(RESPONSE_MESSAGES.INVALID_ADDRESS_400.statusCode)
+    expect(responseData.message).toBe(RESPONSE_MESSAGES.INVALID_ADDRESS_400.message)
+  })
+})
+
 describe('GET /api/address/balance/[address]', () => {
   const baseRequestOptions: RequestOptions = {
     method: 'GET' as RequestMethod,
@@ -1300,6 +1319,22 @@ describe('GET /api/address/balance/[address]', () => {
     const responseData = res._getJSONData()
     expect(responseData.message).toBe(RESPONSE_MESSAGES.ADDRESS_NOT_PROVIDED_400.message)
   })
+
+  it('Should return HTTP 400 when multiple address query parameters are provided', async () => {
+    const requestOptions: RequestOptions = {
+      method: 'GET' as RequestMethod,
+      headers: {
+        'Content-Type': 'application/json'
+      },
+      query: {
+        address: ['address1', 'address2']
+      }
+    }
+    const res = await testEndpoint(requestOptions, balanceEndpoint)
+    const responseData = res._getJSONData()
+    expect(res.statusCode).toBe(RESPONSE_MESSAGES.INVALID_ADDRESS_400.statusCode)
+    expect(responseData.message).toBe(RESPONSE_MESSAGES.INVALID_ADDRESS_400.message)
+  })
 })
 
 describe('GET /api/payments', () => {
diff --git a/tests/unittests/validators.test.ts b/tests/unittests/validators.test.ts
index 6bbf8dd2e..934400eeb 100644
--- a/tests/unittests/validators.test.ts
+++ b/tests/unittests/validators.test.ts
@@ -109,6 +109,12 @@ describe('parseAddress', () => {
       v.parseAddress('')
     }).toThrow(RESPONSE_MESSAGES.ADDRESS_NOT_PROVIDED_400.message)
   })
+
+  it('Reject repeated query parameters passed as an array', () => {
+    expect(() => {
+      v.parseAddress([exampleAddresses.ecash, exampleAddresses.bitcoincash])
+    }).toThrow(RESPONSE_MESSAGES.INVALID_ADDRESS_400.message)
+  })
 })
 
 describe('parseError', () => {
diff --git a/utils/validators.ts b/utils/validators.ts
index 6f4c2eaa6..f8b809817 100644
--- a/utils/validators.ts
+++ b/utils/validators.ts
@@ -28,7 +28,10 @@ const parseAddressTextBlock = function (addressBlock: string): string[] {
     .filter((value, index, self) => self.indexOf(value) === index)
 }
 
-export const parseAddress = function (addressString: string | undefined): string {
+export const parseAddress = function (addressString: string | string[] | undefined): string {
+  // Repeated query keys arrive as arrays. String methods like includes() then
+  // check membership instead of a substring, so reject non-strings before use.
+  if (Array.isArray(addressString)) throw new Error(RESPONSE_MESSAGES.INVALID_ADDRESS_400.message)
   if (addressString === '' || addressString === undefined) throw new Error(RESPONSE_MESSAGES.ADDRESS_NOT_PROVIDED_400.message)
   let parsedAddress: string
   if (