diff --git a/app/models/assignment.rb b/app/models/assignment.rb
index f60eb974d..02f81bc25 100644
--- a/app/models/assignment.rb
+++ b/app/models/assignment.rb
@@ -1,7 +1,18 @@
 class Assignment < ApplicationRecord
+  LIMIT = 10
+
   belongs_to :account, default: -> { card.account }
   belongs_to :card, touch: true
 
   belongs_to :assignee, class_name: "User"
   belongs_to :assigner, class_name: "User"
+
+  validate :within_limit, on: :create
+
+  private
+    def within_limit
+      if card.assignments.count >= LIMIT
+        errors.add(:base, "Card already has the maximum of #{LIMIT} assignees")
+      end
+    end
 end
diff --git a/app/models/card/assignable.rb b/app/models/card/assignable.rb
index be0dd257e..6320faeb3 100644
--- a/app/models/card/assignable.rb
+++ b/app/models/card/assignable.rb
@@ -24,10 +24,12 @@ module Card::Assignable
 
   private
     def assign(user)
-      assignments.create! assignee: user, assigner: Current.user
-      watch_by user
+      assignment = assignments.create assignee: user, assigner: Current.user
 
-      track_event :assigned, assignee_ids: [ user.id ]
+      if assignment.persisted?
+        watch_by user
+        track_event :assigned, assignee_ids: [ user.id ]
+      end
     rescue ActiveRecord::RecordNotUnique
       # Already assigned
     end
diff --git a/test/models/assignment_test.rb b/test/models/assignment_test.rb
index ca8f09a34..3ac309619 100644
--- a/test/models/assignment_test.rb
+++ b/test/models/assignment_test.rb
@@ -1,7 +1,38 @@
 require "test_helper"
 
 class AssignmentTest < ActiveSupport::TestCase
-  # test "the truth" do
-  #   assert true
-  # end
+  test "create" do
+    card = cards(:text)
+    assignment = card.assignments.create!(assignee: users(:david), assigner: users(:jason))
+
+    assert_equal users(:david), assignment.assignee
+    assert_equal users(:jason), assignment.assigner
+    assert_equal card, assignment.card
+  end
+
+  test "create cannot exceed assignee limit" do
+    card = cards(:logo)
+    board = card.board
+    account = card.account
+
+    card.assignments.delete_all
+
+    Assignment::LIMIT.times do |i|
+      identity = Identity.create!(email_address: "limit_test_#{i}@example.com")
+      user = account.users.create!(identity: identity, name: "Limit Test User #{i}", role: :member)
+      user.accesses.find_or_create_by!(board: board)
+      card.assignments.create!(assignee: user, assigner: users(:david))
+    end
+
+    assert_equal Assignment::LIMIT, card.assignments.count
+
+    identity = Identity.create!(email_address: "over_limit@example.com")
+    extra_user = account.users.create!(identity: identity, name: "Over Limit User", role: :member)
+    extra_user.accesses.find_or_create_by!(board: board)
+
+    assignment = card.assignments.build(assignee: extra_user, assigner: users(:david))
+
+    assert_not assignment.valid?
+    assert_includes assignment.errors[:base], "Card already has the maximum of #{Assignment::LIMIT} assignees"
+  end
 end
diff --git a/test/models/card/assignable_test.rb b/test/models/card/assignable_test.rb
index 9d0c1f1c5..6ee8a164d 100644
--- a/test/models/card/assignable_test.rb
+++ b/test/models/card/assignable_test.rb
@@ -12,4 +12,31 @@ class Card::AssignableTest < ActiveSupport::TestCase
     assert cards(:layout).assigned_to?(users(:kevin))
     assert cards(:layout).watched_by?(users(:kevin))
   end
+
+  test "toggle_assignment does not add assignee when at limit" do
+    card = cards(:logo)
+    board = card.board
+    account = card.account
+
+    card.assignments.delete_all
+
+    Assignment::LIMIT.times do |i|
+      identity = Identity.create!(email_address: "toggle_test_#{i}@example.com")
+      user = account.users.create!(identity: identity, name: "Toggle Test User #{i}", role: :member)
+      user.accesses.find_or_create_by!(board: board)
+      card.assignments.create!(assignee: user, assigner: users(:david))
+    end
+
+    identity = Identity.create!(email_address: "toggle_over@example.com")
+    extra_user = account.users.create!(identity: identity, name: "Toggle Over User", role: :member)
+    extra_user.accesses.find_or_create_by!(board: board)
+
+    with_current_user(:david) do
+      assert_no_difference "card.assignments.count" do
+        card.toggle_assignment(extra_user)
+      end
+    end
+
+    assert_not card.reload.assigned_to?(extra_user)
+  end
 end