diff --git a/commands/addons/attach.js b/commands/addons/attach.js
index 95b6885..9f7ff7f 100644
--- a/commands/addons/attach.js
+++ b/commands/addons/attach.js
@@ -29,6 +29,13 @@ function * run (context, heroku) {
     )
   }
 
+  if (context.flags.credential) {
+    let credentialConfig = yield heroku.get(`/addons/${addon.name}/config/credential:${context.flags.credential}`)
+    if (credentialConfig.length === 0) {
+      throw new Error(`Could not find credential ${context.flags.credential} for database ${addon.name}`)
+    }
+  }
+
   let attachment = yield util.trapConfirmationRequired(context.app, context.flags.confirm, (confirm) => createAttachment(app, context.flags.as, confirm, context.flags.credential))
 
   yield cli.action(
diff --git a/test/commands/addons/attach.js b/test/commands/addons/attach.js
index 220678c..7c3d115 100644
--- a/test/commands/addons/attach.js
+++ b/test/commands/addons/attach.js
@@ -72,6 +72,8 @@ Setting foo config vars and restarting myapp... done, v10
     let api = nock('https://api.heroku.com:443')
       .get('/addons/postgres-123')
       .reply(200, {name: 'postgres-123'})
+      .get('/addons/postgres-123/config/credential:hello')
+      .reply(200, [{some: 'config'}])
       .post('/addon-attachments', {app: {name: 'myapp'}, addon: {name: 'postgres-123'}, namespace: 'credential:hello'})
       .reply(201, {name: 'POSTGRES_HELLO'})
       .get('/apps/myapp/releases')
@@ -83,4 +85,18 @@ Setting POSTGRES_HELLO config vars and restarting myapp... done, v10
 `))
       .then(() => api.done())
   })
+
+  it('errors if the credential flag is specified but that credential does not exist for that addon', function () {
+    nock('https://api.heroku.com:443')
+      .get('/addons/postgres-123')
+      .reply(200, {name: 'postgres-123'})
+      .get('/addons/postgres-123/config/credential:hello')
+      .reply(200, [])
+
+    return expect(cmd.run({
+      app: 'myapp',
+      args: {addon_name: 'postgres-123'},
+      flags: {credential: 'hello'}
+    }), 'to be rejected with error satisfying', new Error('Could not find credential hello for database postgres-123'))
+  })
 })