diff --git a/lib/spree/chimpy/interface/customer_upserter.rb b/lib/spree/chimpy/interface/customer_upserter.rb
index 59690d9..26af94c 100644
--- a/lib/spree/chimpy/interface/customer_upserter.rb
+++ b/lib/spree/chimpy/interface/customer_upserter.rb
@@ -39,6 +39,8 @@ def customer_id_from_eid(mc_eid)
       private
 
       def upsert_customer
+        return unless @order.user_id
+
         customer_id = self.class.mailchimp_customer_id(@order.user_id)
         begin
           response = store_api_call
diff --git a/lib/spree/chimpy/interface/order_upserter.rb b/lib/spree/chimpy/interface/order_upserter.rb
index 5c7ec4c..a0ed0a1 100644
--- a/lib/spree/chimpy/interface/order_upserter.rb
+++ b/lib/spree/chimpy/interface/order_upserter.rb
@@ -7,8 +7,15 @@ def initialize(order)
         @order = order
       end
 
+      def customer_id
+        @customer_id ||= CustomerUpserter.new(@order).ensure_customer
+      end
+
       def upsert
+        return unless customer_id
+
         Products.ensure_products(@order)
+
         perform_upsert
       end
 
@@ -52,7 +59,6 @@ def order_variant_hash(line_item)
       end
 
       def order_hash
-        customer_id = CustomerUpserter.new(@order).ensure_customer
         source = @order.source
 
         lines = @order.line_items.map do |line|
diff --git a/spec/lib/customers_interface_spec.rb b/spec/lib/customers_interface_spec.rb
index 183f4ee..e7cca15 100644
--- a/spec/lib/customers_interface_spec.rb
+++ b/spec/lib/customers_interface_spec.rb
@@ -40,14 +40,23 @@
       expect(interface.ensure_customer).to eq "customer_999"
     end
 
-    it "upserts the customer when not found by order source" do
-      allow(interface).to receive(:customer_id_from_eid)
-        .with('id-abcd')
-        .and_return(nil)
+    context "when no customer from order source" do
+      before(:each) do
+        allow(interface).to receive(:customer_id_from_eid)
+          .with('id-abcd')
+          .and_return(nil)
+      end
 
-      allow(interface).to receive(:upsert_customer) { "customer_998" }
+      it "upserts the customer" do
+        allow(interface).to receive(:upsert_customer) { "customer_998" }
 
-      expect(interface.ensure_customer).to eq "customer_998"
+        expect(interface.ensure_customer).to eq "customer_998"
+      end
+
+      it "returns nil if guest checkout" do
+        order.user_id = nil
+        expect(interface.ensure_customer).to be_nil
+      end
     end
   end
 
diff --git a/spec/lib/order_upserter_spec.rb b/spec/lib/order_upserter_spec.rb
index fdb163c..e5be979 100644
--- a/spec/lib/order_upserter_spec.rb
+++ b/spec/lib/order_upserter_spec.rb
@@ -73,6 +73,15 @@ def check_hash(h, expected_customer_id)
       interface.upsert
     end
 
+    it "does not perform the order upsert if no customer_id exists" do
+      expect(customer_upserter).to receive(:ensure_customer)
+        .and_return(nil)
+
+      expect(interface).to_not receive(:perform_upsert)
+
+      interface.upsert
+    end
+
     context "when order already exists" do
       before(:each) do
         allow(order_api).to receive(:retrieve)