diff --git a/src/api/groups.js b/src/api/groups.js
index 95074c4b6a..55e1ca10cd 100644
--- a/src/api/groups.js
+++ b/src/api/groups.js
@@ -118,19 +118,16 @@ async function canSearchMembers(uid, groupName) {
 	}
 }
 
-groupsAPI.join = async function (caller, data) {
+function validateJoinRequest(caller, data) {
 	if (!data) {
 		throw new Error('[[error:invalid-data]]');
 	}
 	if (caller.uid <= 0 || !data.uid) {
 		throw new Error('[[error:invalid-uid]]');
 	}
+}
 
-	const groupName = await groups.getGroupNameByGroupSlug(data.slug);
-	if (!groupName) {
-		throw new Error('[[error:no-group]]');
-	}
-
+async function checkPrivileges(caller, groupName) {
 	const isCallerAdmin = await privileges.admin.can('admin:groups', caller.uid);
 	if (!isCallerAdmin && (
 		groups.systemGroups.includes(groupName) ||
@@ -138,6 +135,22 @@ groupsAPI.join = async function (caller, data) {
 	)) {
 		throw new Error('[[error:not-allowed]]');
 	}
+	return isCallerAdmin;
+}
+
+function isGroupJoinDisabledForCaller(isCallerAdmin, isSelf, groupData) {
+	return !isCallerAdmin && isSelf && groupData.private && groupData.disableJoinRequests;
+}
+
+groupsAPI.join = async function (caller, data) {
+	validateJoinRequest(caller, data);
+
+	const groupName = await groups.getGroupNameByGroupSlug(data.slug);
+	if (!groupName) {
+		throw new Error('[[error:no-group]]');
+	}
+
+	const isCallerAdmin = await checkPrivileges(caller, groupName);
 
 	const [groupData, userExists] = await Promise.all([
 		groups.getGroupData(groupName),
@@ -159,7 +172,7 @@ groupsAPI.join = async function (caller, data) {
 		return;
 	}
 
-	if (!isCallerAdmin && isSelf && groupData.private && groupData.disableJoinRequests) {
+	if (isGroupJoinDisabledForCaller(isCallerAdmin, isSelf, groupData)) {
 		throw new Error('[[error:group-join-disabled]]');
 	}
 
diff --git a/test/groups.js b/test/groups.js
index 7b5ae4d73c..f36dc13a51 100644
--- a/test/groups.js
+++ b/test/groups.js
@@ -1021,6 +1021,16 @@ describe('Groups', () => {
 			assert.equal(updatedData.private, false);
 		});
 
+		it('should fail to join group if user does not exist', async () => {
+			const nonExistentUid = 123456789;
+			try {
+				await apiGroups.join({ uid: adminUid }, { uid: nonExistentUid, slug: 'test' });
+				assert(false);
+			} catch (err) {
+				assert.strictEqual(err.message, '[[error:invalid-uid]]');
+			}
+		});
+
 		it('should fail to create a group with name guests', async () => {
 			try {
 				await apiGroups.create({ uid: adminUid }, { name: 'guests' });