diff --git a/apps/portal/README.md b/apps/portal/README.md
index fa568b4099..6f4591d74b 100644
--- a/apps/portal/README.md
+++ b/apps/portal/README.md
@@ -48,6 +48,8 @@ Open [http://localhost:3000](http://localhost:3000) to view it in the browser.
 The page will reload if you make edits.<br />
 You will also see any lint errors in the console.
 
+Start the portal server when developing Ghost by running Ghost (in root folder) via `yarn dev --all` or `yarn dev --portal`. This will host the portal JavaScript files, and makes sure that Ghost uses these locally hosted assets instead of the ones from the CDN.
+
 ### `yarn build`
 
 Creates the production single minified bundle for external use in `umd/portal.min.js`.  <br />
diff --git a/ghost/members-api/lib/repositories/MemberRepository.js b/ghost/members-api/lib/repositories/MemberRepository.js
index bbcd2d315f..3019f331e5 100644
--- a/ghost/members-api/lib/repositories/MemberRepository.js
+++ b/ghost/members-api/lib/repositories/MemberRepository.js
@@ -18,7 +18,8 @@ const messages = {
     productNotFound: 'Could not find Product {id}',
     bulkActionRequiresFilter: 'Cannot perform {action} without a filter or all=true',
     tierArchived: 'Cannot use archived Tiers',
-    invalidEmail: 'Invalid Email'
+    invalidEmail: 'Invalid Email',
+    invalidNewsletterId: 'Cannot subscribe to invalid newsletter {id}'
 };
 
 /**
@@ -281,7 +282,18 @@ module.exports = class MemberRepository {
             memberStatusData.status = 'comped';
         }
 
-        // Subscribe member to default newsletters
+        //checks for custom signUp forms
+        if (memberData.newsletters && memberData.newsletters.length > 0) {
+            const savedNewsletter = await this._newslettersService.browse({filter: `id:'${memberData.newsletters[0].id}'`});
+            if (savedNewsletter.length === 0) {
+                throw new errors.BadRequestError({message: tpl(messages.invalidNewsletterId, {id: memberData.newsletters[0].id})});
+            }
+            if (savedNewsletter[0].status === 'archived') {
+                memberData.newsletters = [];
+            }
+        }
+
+        // Subscribe members to default newsletters
         if (memberData.subscribed !== false && !memberData.newsletters) {
             const browseOptions = _.pick(options, 'transacting');
             memberData.newsletters = await this.getSubscribeOnSignupNewsletters(browseOptions);
diff --git a/ghost/members-api/test/unit/lib/repositories/member.test.js b/ghost/members-api/test/unit/lib/repositories/member.test.js
index 0baf70977d..35b639013b 100644
--- a/ghost/members-api/test/unit/lib/repositories/member.test.js
+++ b/ghost/members-api/test/unit/lib/repositories/member.test.js
@@ -310,4 +310,134 @@ describe('MemberRepository', function () {
             })).should.be.true();
         });
     });
+
+    describe('create', function () {
+        let memberStub, memberModelStub, newslettersServiceStub;
+
+        beforeEach(function () {
+            memberStub = {
+                get: sinon.stub(),
+                related: sinon.stub()
+            };
+
+            memberStub.related
+                .withArgs('products').returns({
+                    models: []
+                })
+                .withArgs('newsletters').returns({
+                    models: []
+                });
+
+            memberModelStub = {
+                add: sinon.stub().resolves(memberStub)
+            };
+
+            newslettersServiceStub = {
+                browse: sinon.stub()
+            };
+        });
+
+        it('subscribes a member to a specified newsletter', async function () {
+            const newsletter = {
+                id: 'abc123',
+                status: 'active'
+            };
+
+            newslettersServiceStub.browse
+                .withArgs({
+                    filter: `id:'${newsletter.id}'`
+                })
+                .resolves([newsletter]);
+
+            const repo = new MemberRepository({
+                Member: memberModelStub,
+                MemberStatusEvent: {
+                    add: sinon.stub().resolves()
+                },
+                MemberSubscribeEvent: {
+                    add: sinon.stub().resolves()
+                },
+                newslettersService: newslettersServiceStub
+            });
+
+            await repo.create({
+                email: 'jamie@example.com',
+                email_disabled: false,
+                newsletters: [
+                    {id: newsletter.id}
+                ]
+            });
+
+            newslettersServiceStub.browse.calledOnce.should.be.true();
+            memberModelStub.add.calledOnce.should.be.true();
+            memberModelStub.add.args[0][0].newsletters.should.eql([
+                {id: newsletter.id}
+            ]);
+        });
+
+        it('does not allow a member to be subscribed to an invalid newsletter', async function () {
+            const INVALID_NEWSLETTER_ID = 'abc123';
+
+            newslettersServiceStub.browse
+                .withArgs({
+                    filter: `id:'${INVALID_NEWSLETTER_ID}'`
+                })
+                .resolves([]);
+
+            const repo = new MemberRepository({
+                Member: memberModelStub,
+                MemberStatusEvent: {
+                    add: sinon.stub().resolves()
+                },
+                MemberSubscribeEvent: {
+                    add: sinon.stub().resolves()
+                },
+                newslettersService: newslettersServiceStub
+            });
+
+            await repo.create({
+                email: 'jamie@example.com',
+                email_disabled: false,
+                newsletters: [
+                    {id: INVALID_NEWSLETTER_ID}
+                ]
+            }).should.be.rejectedWith(`Cannot subscribe to invalid newsletter ${INVALID_NEWSLETTER_ID}`);
+        });
+
+        it('does not subscribe a member to an archived newsletter', async function () {
+            const newsletter = {
+                id: 'abc123',
+                status: 'archived'
+            };
+
+            newslettersServiceStub.browse
+                .withArgs({
+                    filter: `id:'${newsletter.id}'`
+                })
+                .resolves([newsletter]);
+
+            const repo = new MemberRepository({
+                Member: memberModelStub,
+                MemberStatusEvent: {
+                    add: sinon.stub().resolves()
+                },
+                MemberSubscribeEvent: {
+                    add: sinon.stub().resolves()
+                },
+                newslettersService: newslettersServiceStub
+            });
+
+            await repo.create({
+                email: 'jamie@example.com',
+                email_disabled: false,
+                newsletters: [
+                    {id: newsletter.id}
+                ]
+            });
+
+            newslettersServiceStub.browse.calledOnce.should.be.true();
+            memberModelStub.add.calledOnce.should.be.true();
+            memberModelStub.add.args[0][0].newsletters.should.eql([]);
+        });
+    });
 });