diff --git a/common/locales/en/api-v3.json b/common/locales/en/api-v3.json
index cdb6718327..a2495529e7 100644
--- a/common/locales/en/api-v3.json
+++ b/common/locales/en/api-v3.json
@@ -73,5 +73,6 @@
   "questNotFound": "Quest \"<%= key %>\" not found.",
   "questNotOwned": "You don't own that quest scroll.",
   "questLevelTooHigh": "You must be Level <%= level %> to begin this quest.",
-  "questAlreadyUnderway": "Your party is already on a quest. Try again when the current quest has ended."
+  "questAlreadyUnderway": "Your party is already on a quest. Try again when the current quest has ended.",
+  "questAlreadyAccepted": "You already accepted the quest invitation."
 }
diff --git a/test/api/v3/integration/quests/POST-groups_groupId_quests_accept.test.js b/test/api/v3/integration/quests/POST-groups_groupId_quests_accept.test.js
index e218d7e3d9..665a185279 100644
--- a/test/api/v3/integration/quests/POST-groups_groupId_quests_accept.test.js
+++ b/test/api/v3/integration/quests/POST-groups_groupId_quests_accept.test.js
@@ -1,27 +1,37 @@
 import {
   createAndPopulateGroup,
   translate as t,
+  generateUser,
 } from '../../../../helpers/api-v3-integration.helper';
 
-describe.skip('POST /groups/:groupId/quests/accept', () => {
+describe('POST /groups/:groupId/quests/accept', () => {
+  const PET_QUEST = 'whale';
+
   let questingGroup;
   let leader;
-  let member;
+  let partyMembers;
+  let user;
 
   beforeEach(async () => {
+    user = await generateUser();
+
     let { group, groupLeader, members } = await createAndPopulateGroup({
       groupDetails: { type: 'party', privacy: 'private' },
-      members: 1,
+      members: 2,
     });
 
     questingGroup = group;
     leader = groupLeader;
-    member = members[0];
+    partyMembers = members;
+
+    await leader.update({
+      [`items.quests.${PET_QUEST}`]: 1,
+    });
   });
 
   context('failure conditions', () => {
     it('does not accept quest without an invite', async () => {
-      await expect(leader.post(`/groups/${questingGroup._id}/quests/accept`, {}))
+      await expect(leader.post(`/groups/${questingGroup._id}/quests/accept`))
       .to.eventually.be.rejected.and.eql({
         code: 404,
         error: 'NotFound',
@@ -30,25 +40,80 @@ describe.skip('POST /groups/:groupId/quests/accept', () => {
     });
 
     it('does not accept quest for a group in which user is not a member', async () => {
-      await expect(member.post(`/groups/${questingGroup._id}/quests/accept`, {}))
+      await expect(user.post(`/groups/${questingGroup._id}/quests/accept`))
       .to.eventually.be.rejected.and.eql({
         code: 404,
         error: 'NotFound',
-        message: t('questInviteNotFound'),
+        message: t('groupNotFound'),
+      });
+    });
+
+    it('does not accept quest for a guild', async () => {
+      let { group: guild, groupLeader: guildLeader } = await createAndPopulateGroup({
+        groupDetails: { type: 'guild', privacy: 'private' },
+      });
+
+      await expect(guildLeader.post(`/groups/${guild._id}/quests/accept`))
+      .to.eventually.be.rejected.and.eql({
+        code: 401,
+        error: 'NotAuthorized',
+        message: t('guildQuestsNotSupported'),
+      });
+    });
+
+    it('does not accept invite twice', async () => {
+      await leader.post(`/groups/${questingGroup._id}/quests/invite/${PET_QUEST}`);
+      await partyMembers[0].post(`/groups/${questingGroup._id}/quests/accept`);
+
+      await expect(partyMembers[0].post(`/groups/${questingGroup._id}/quests/accept`))
+      .to.eventually.be.rejected.and.eql({
+        code: 400,
+        error: 'BadRequest',
+        message: t('questAlreadyAccepted'),
+      });
+    });
+
+    it('does not accept invite for a quest already underway', async () => {
+      await leader.post(`/groups/${questingGroup._id}/quests/invite/${PET_QUEST}`);
+      await partyMembers[0].post(`/groups/${questingGroup._id}/quests/accept`);
+      // quest will start after everyone has accepted
+      await partyMembers[1].post(`/groups/${questingGroup._id}/quests/accept`);
+
+      await expect(partyMembers[0].post(`/groups/${questingGroup._id}/quests/accept`))
+      .to.eventually.be.rejected.and.eql({
+        code: 401,
+        error: 'NotAuthorized',
+        message: t('questAlreadyUnderway'),
       });
     });
   });
+
   context('successfully accepting a quest invitation', () => {
-    it('joins a quest from an invitation', () => {
+    it('joins a quest from an invitation', async () => {
+      await leader.post(`/groups/${questingGroup._id}/quests/invite/${PET_QUEST}`);
+      await partyMembers[0].post(`/groups/${questingGroup._id}/quests/accept`);
 
+      await Promise.all([partyMembers[0].sync(), questingGroup.sync()]);
+      expect(leader.party.quest.RSVPNeeded).to.equal(false);
+      expect(questingGroup.quest.members[partyMembers[0]._id]);
     });
 
-    it('does not begin the quest if pending invitations remain', () => {
+    it('does not begin the quest if pending invitations remain', async () => {
+      await leader.post(`/groups/${questingGroup._id}/quests/invite/${PET_QUEST}`);
+      await partyMembers[0].post(`/groups/${questingGroup._id}/quests/accept`);
 
+      await questingGroup.sync();
+      expect(questingGroup.quest.active).to.equal(false);
     });
 
-    it('begins the quest if accepting the last pending invite', () => {
+    it('begins the quest if accepting the last pending invite', async () => {
+      await leader.post(`/groups/${questingGroup._id}/quests/invite/${PET_QUEST}`);
+      await partyMembers[0].post(`/groups/${questingGroup._id}/quests/accept`);
+      // quest will start after everyone has accepted
+      await partyMembers[1].post(`/groups/${questingGroup._id}/quests/accept`);
 
+      await questingGroup.sync();
+      expect(questingGroup.quest.active).to.equal(true);
     });
   });
 });
diff --git a/website/src/controllers/api-v3/quests.js b/website/src/controllers/api-v3/quests.js
index 13584b139c..162954b7dd 100644
--- a/website/src/controllers/api-v3/quests.js
+++ b/website/src/controllers/api-v3/quests.js
@@ -12,6 +12,7 @@ import {
 import {
   NotFound,
   NotAuthorized,
+  BadRequest,
 } from '../../libs/api-v3/errors';
 import {
   getUserInfo,
@@ -151,7 +152,10 @@ api.acceptQuest = {
     if (!group) throw new NotFound(res.t('groupNotFound'));
     if (group.type !== 'party') throw new NotAuthorized(res.t('guildQuestsNotSupported'));
     if (!group.quest.key) throw new NotFound(res.t('questInviteNotFound'));
+    if (group.quest.active) throw new NotAuthorized(res.t('questAlreadyUnderway'));
+    if (group.quest.members[user._id]) throw new BadRequest(res.t('questAlreadyAccepted'));
 
+    group.markModified('quest');
     group.quest.members[user._id] = true;
     user.party.quest.RSVPNeeded = false;