diff --git a/app/builders/agent_builder.rb b/app/builders/agent_builder.rb
index d2715011c..af68eefc5 100644
--- a/app/builders/agent_builder.rb
+++ b/app/builders/agent_builder.rb
@@ -2,6 +2,14 @@
 # It initializes with necessary attributes and provides a perform method
 # to create a user and account user in a transaction.
 class AgentBuilder
+  LIMIT_EXCEEDED_MESSAGE = 'Account limit exceeded. Please purchase more licenses'.freeze
+
+  class LimitExceededError < StandardError
+    def initialize
+      super(AgentBuilder::LIMIT_EXCEEDED_MESSAGE)
+    end
+  end
+
   # Initializes an AgentBuilder with necessary attributes.
   # @param email [String] the email of the user.
   # @param name [String] the name of the user.
@@ -14,15 +22,23 @@ class AgentBuilder
   # Creates a user and account user in a transaction.
   # @return [User] the created user.
   def perform
-    ActiveRecord::Base.transaction do
-      @user = find_or_create_user
-      create_account_user
+    account.with_lock do
+      raise LimitExceededError unless can_add_agent?
+
+      ActiveRecord::Base.transaction do
+        @user = find_or_create_user
+        create_account_user
+      end
     end
     @user
   end
 
   private
 
+  def can_add_agent?
+    account.usage_limits[:agents] > account.account_users.count
+  end
+
   # Finds a user by email or creates a new one with a temporary password.
   # @return [User] the found or created user.
   def find_or_create_user
diff --git a/app/controllers/api/v1/accounts/agents_controller.rb b/app/controllers/api/v1/accounts/agents_controller.rb
index 438944f04..864c50bb4 100644
--- a/app/controllers/api/v1/accounts/agents_controller.rb
+++ b/app/controllers/api/v1/accounts/agents_controller.rb
@@ -1,8 +1,6 @@
 class Api::V1::Accounts::AgentsController < Api::V1::Accounts::BaseController
   before_action :fetch_agent, except: [:create, :index, :bulk_create]
   before_action :check_authorization
-  before_action :validate_limit, only: [:create]
-  before_action :validate_limit_for_bulk_create, only: [:bulk_create]
 
   def index
     @agents = agents
@@ -20,6 +18,8 @@ class Api::V1::Accounts::AgentsController < Api::V1::Accounts::BaseController
     )
 
     @agent = builder.perform
+  rescue AgentBuilder::LimitExceededError => e
+    render_payment_required(e.message)
   end
 
   def update
@@ -36,25 +36,13 @@ class Api::V1::Accounts::AgentsController < Api::V1::Accounts::BaseController
   def bulk_create
     emails = params[:emails]
 
-    emails.each do |email|
-      builder = AgentBuilder.new(
-        email: email,
-        name: email.split('@').first,
-        inviter: current_user,
-        account: Current.account
-      )
-      begin
-        builder.perform
-      rescue ActiveRecord::RecordInvalid => e
-        Rails.logger.info "[Agent#bulk_create] ignoring email #{email}, errors: #{e.record.errors}"
-      end
-    end
-
+    bulk_create_agents(emails)
     # This endpoint is used to bulk create agents during onboarding
     # onboarding_step key in present in Current account custom attributes, since this is a one time operation
-    Current.account.custom_attributes.delete('onboarding_step')
-    Current.account.save!
+    clear_onboarding_step
     head :ok
+  rescue AgentBuilder::LimitExceededError => e
+    render_payment_required(e.message)
   end
 
   private
@@ -87,22 +75,33 @@ class Api::V1::Accounts::AgentsController < Api::V1::Accounts::BaseController
     @agents ||= Current.account.users.order_by_full_name.includes(:account_users, { avatar_attachment: [:blob] })
   end
 
-  def validate_limit_for_bulk_create
-    limit_available = params[:emails].count <= available_agent_count
+  def bulk_create_agents(emails)
+    Current.account.with_lock do
+      raise AgentBuilder::LimitExceededError if emails.count > available_agent_count
 
-    render_payment_required('Account limit exceeded. Please purchase more licenses') unless limit_available
+      emails.each { |email| create_agent_from_email(email) }
+    end
   end
 
-  def validate_limit
-    render_payment_required('Account limit exceeded. Please purchase more licenses') unless can_add_agent?
+  def create_agent_from_email(email)
+    builder = AgentBuilder.new(
+      email: email,
+      name: email.split('@').first,
+      inviter: current_user,
+      account: Current.account
+    )
+    builder.perform
+  rescue ActiveRecord::RecordInvalid => e
+    Rails.logger.info "[Agent#bulk_create] ignoring email #{email}, errors: #{e.record.errors}"
+  end
+
+  def clear_onboarding_step
+    Current.account.custom_attributes.delete('onboarding_step')
+    Current.account.save!
   end
 
   def available_agent_count
-    Current.account.usage_limits[:agents] - agents.count
-  end
-
-  def can_add_agent?
-    available_agent_count.positive?
+    Current.account.usage_limits[:agents] - Current.account.account_users.count
   end
 
   def delete_user_record(agent)
diff --git a/enterprise/app/controllers/enterprise/api/v1/accounts/agents_controller.rb b/enterprise/app/controllers/enterprise/api/v1/accounts/agents_controller.rb
index b3a27c4ad..02d027b58 100644
--- a/enterprise/app/controllers/enterprise/api/v1/accounts/agents_controller.rb
+++ b/enterprise/app/controllers/enterprise/api/v1/accounts/agents_controller.rb
@@ -1,6 +1,8 @@
 module Enterprise::Api::V1::Accounts::AgentsController
   def create
     super
+    return if @agent.blank?
+
     associate_agent_with_custom_role
   end
 
diff --git a/spec/builders/agent_builder_spec.rb b/spec/builders/agent_builder_spec.rb
index f140f2f29..69cacb22b 100644
--- a/spec/builders/agent_builder_spec.rb
+++ b/spec/builders/agent_builder_spec.rb
@@ -23,6 +23,12 @@ RSpec.describe AgentBuilder, type: :model do
   end
 
   describe '#perform' do
+    it 'locks the account while checking and creating the agent' do
+      expect(account).to receive(:with_lock).and_call_original
+
+      agent_builder.perform
+    end
+
     context 'when user does not exist' do
       it 'creates a new user' do
         expect { agent_builder.perform }.to change(User, :count).by(1)
@@ -67,5 +73,17 @@ RSpec.describe AgentBuilder, type: :model do
         expect(user.encrypted_password).not_to be_empty
       end
     end
+
+    context 'when the account has reached its agent limit' do
+      before do
+        allow(account).to receive(:usage_limits).and_return({ agents: account.account_users.count })
+      end
+
+      it 'raises a limit exceeded error without creating a user' do
+        expect { agent_builder.perform }.to raise_error(described_class::LimitExceededError, described_class::LIMIT_EXCEEDED_MESSAGE)
+
+        expect(User.from_email(email)).to be_nil
+      end
+    end
   end
 end
diff --git a/spec/enterprise/controllers/api/v1/accounts/agents_controller_spec.rb b/spec/enterprise/controllers/api/v1/accounts/agents_controller_spec.rb
index e5a8a5b7d..270150979 100644
--- a/spec/enterprise/controllers/api/v1/accounts/agents_controller_spec.rb
+++ b/spec/enterprise/controllers/api/v1/accounts/agents_controller_spec.rb
@@ -21,6 +21,27 @@ RSpec.describe 'Agents API', type: :request do
         expect(response).to have_http_status(:payment_required)
         expect(response.body).to include('Account limit exceeded. Please purchase more licenses')
       end
+
+      it 'prevents adding an agent if the last seat is consumed before creation' do
+        account.update!(limits: { agents: account.account_users.count + 1 })
+        competing_agent_created = false
+
+        allow(AgentBuilder).to receive(:new).and_wrap_original do |method, *args|
+          unless competing_agent_created
+            create(:user, account: account, role: :agent)
+            competing_agent_created = true
+          end
+
+          method.call(*args)
+        end
+
+        post "/api/v1/accounts/#{account.id}/agents", params: params, headers: admin.create_new_auth_token, as: :json
+
+        expect(response).to have_http_status(:payment_required)
+        expect(response.body).to include('Account limit exceeded. Please purchase more licenses')
+        expect(User.from_email(params[:email])).to be_nil
+        expect(account.account_users.count).to eq(account.usage_limits[:agents])
+      end
     end
   end