diff --git a/app/models/concerns/user_subscription_sourceable.rb b/app/models/concerns/user_subscription_sourceable.rb
index ddce09ec4..8da63d462 100644
--- a/app/models/concerns/user_subscription_sourceable.rb
+++ b/app/models/concerns/user_subscription_sourceable.rb
@@ -4,7 +4,7 @@ module UserSubscriptionSourceable
   # This all assumes there's an association with User under the column user_id.
 
   included do
-    has_many :user_subscriptions, as: :user_subscription_sourceable
+    has_many :user_subscriptions, as: :user_subscription_sourceable, dependent: :nullify
     has_many :sourced_subscribers,
              class_name: "User",
              through: :user_subscriptions,
diff --git a/app/models/user_subscription.rb b/app/models/user_subscription.rb
index 9d306d250..29fb211cc 100644
--- a/app/models/user_subscription.rb
+++ b/app/models/user_subscription.rb
@@ -9,14 +9,23 @@ class UserSubscription < ApplicationRecord
 
   belongs_to :author, class_name: "User", inverse_of: :source_authored_user_subscriptions
   belongs_to :subscriber, class_name: "User", inverse_of: :subscribed_to_user_subscriptions
-  belongs_to :user_subscription_sourceable, polymorphic: true
+  belongs_to :user_subscription_sourceable, polymorphic: true, optional: true
 
   validates :author_id, presence: true
+
   validates :subscriber_email, presence: true
-  validates :subscriber_id, presence: true, uniqueness: { scope: %i[subscriber_email user_subscription_sourceable_type
-                                                                    user_subscription_sourceable_id] }
-  validates :user_subscription_sourceable_id, presence: true
-  validates :user_subscription_sourceable_type, presence: true, inclusion: { in: ALLOWED_TYPES }
+  validates :subscriber_id, presence: true, uniqueness: {
+    scope: %i[subscriber_email user_subscription_sourceable_type user_subscription_sourceable_id]
+  }
+
+  validates :user_subscription_sourceable_id, presence: true, on: :create
+  validates :user_subscription_sourceable_id, presence: true, on: :update, if: :user_subscription_sourceable_type
+  validates :user_subscription_sourceable_type, presence: true, on: :create
+  validates :user_subscription_sourceable_type, presence: true, on: :update, if: :user_subscription_sourceable_id
+
+  validates :user_subscription_sourceable_type, inclusion: { in: ALLOWED_TYPES }, on: :create
+  validates :user_subscription_sourceable_type,
+            inclusion: { in: ALLOWED_TYPES }, on: :update, if: :user_subscription_sourceable_id
 
   validate :tag_enabled
   validate :non_apple_auth_subscriber
diff --git a/db/migrate/20200827073520_set_user_subscription_sourceable_columns_to_null.rb b/db/migrate/20200827073520_set_user_subscription_sourceable_columns_to_null.rb
new file mode 100644
index 000000000..de8119dad
--- /dev/null
+++ b/db/migrate/20200827073520_set_user_subscription_sourceable_columns_to_null.rb
@@ -0,0 +1,6 @@
+class SetUserSubscriptionSourceableColumnsToNull < ActiveRecord::Migration[6.0]
+  def change
+    change_column_null :user_subscriptions, :user_subscription_sourceable_id, true
+    change_column_null :user_subscriptions, :user_subscription_sourceable_type, true
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index c1083a906..d63972c6a 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2020_08_22_092853) do
+ActiveRecord::Schema.define(version: 2020_08_27_073520) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "citext"
@@ -1161,8 +1161,8 @@ ActiveRecord::Schema.define(version: 2020_08_22_092853) do
     t.string "subscriber_email", null: false
     t.bigint "subscriber_id", null: false
     t.datetime "updated_at", precision: 6, null: false
-    t.bigint "user_subscription_sourceable_id", null: false
-    t.string "user_subscription_sourceable_type", null: false
+    t.bigint "user_subscription_sourceable_id"
+    t.string "user_subscription_sourceable_type"
     t.index ["author_id"], name: "index_user_subscriptions_on_author_id"
     t.index ["subscriber_email"], name: "index_user_subscriptions_on_subscriber_email"
     t.index ["subscriber_id", "subscriber_email", "user_subscription_sourceable_type", "user_subscription_sourceable_id"], name: "index_subscriber_id_and_email_with_user_subscription_source", unique: true
diff --git a/spec/models/user_subscription_spec.rb b/spec/models/user_subscription_spec.rb
index 5ec7581c6..5545804a4 100644
--- a/spec/models/user_subscription_spec.rb
+++ b/spec/models/user_subscription_spec.rb
@@ -44,6 +44,28 @@ RSpec.describe UserSubscription, type: :model do
       error = "Can't subscribe with an Apple private relay. Please update email."
       expect(user_subscription.errors[:subscriber_email]).to include(error)
     end
+
+    describe "#user_subscription_sourceable" do
+      it "is required on creation" do
+        subscription = described_class.new(
+          user_subscription_sourceable: nil, subscriber: subscriber, subscriber_email: subscriber.email,
+          author: source.user
+        )
+        subscription.save
+
+        expect(subscription).not_to be_valid
+        expect(subscription.errors.messages.keys).to include(
+          :user_subscription_sourceable_id, :user_subscription_sourceable_type
+        )
+      end
+
+      it "can be nulled on update" do
+        subscription = described_class.make(source: source, subscriber: subscriber)
+        subscription.update(user_subscription_sourceable: nil)
+
+        expect(subscription).to be_valid
+      end
+    end
   end
 
   describe "#build" do