diff --git a/framework/shopify/cart/use-add-item.tsx b/framework/shopify/cart/use-add-item.tsx
index c17462cc0..6dc3b8d6a 100644
--- a/framework/shopify/cart/use-add-item.tsx
+++ b/framework/shopify/cart/use-add-item.tsx
@@ -3,18 +3,10 @@ import { CommerceError } from '@commerce/utils/errors'
 import useAddItem, { UseAddItem } from '@commerce/cart/use-add-item'
 import useCart from './use-cart'
 import { ShopifyProvider } from '..'
-import { AddCartItemBody, CartItemBody } from '@commerce/types'
-import { Cart } from '@framework/types'
-import {
-  checkoutLineItemAddMutation,
-  getCheckoutId,
-  getCheckoutQuery,
-} from '@framework/utils'
+import { Cart, AddCartItemBody, CartItemBody } from '../types'
+import { checkoutLineItemAddMutation, getCheckoutId } from '../utils'
 import { checkoutToCart } from './utils'
-
-const defaultOpts = {
-  query: checkoutLineItemAddMutation,
-}
+import { Mutation } from '../schema'
 
 export default useAddItem as UseAddItem<ShopifyProvider, CartItemBody>
 
@@ -22,8 +14,7 @@ export const handler: MutationHandler<Cart, {}, AddCartItemBody> = {
   fetchOptions: {
     query: checkoutLineItemAddMutation,
   },
-  async fetcher({ input, options, fetch }) {
-    const item = input.item ?? input
+  async fetcher({ input: { item }, options, fetch }) {
     if (
       item.quantity &&
       (!Number.isInteger(item.quantity) || item.quantity! < 1)
@@ -33,8 +24,7 @@ export const handler: MutationHandler<Cart, {}, AddCartItemBody> = {
       })
     }
 
-    const data = await fetch<any, any>({
-      ...defaultOpts,
+    const { checkoutLineItemsAdd }: Mutation = await fetch<any, any>({
       ...options,
       variables: {
         lineItems: [
@@ -47,7 +37,7 @@ export const handler: MutationHandler<Cart, {}, AddCartItemBody> = {
       },
     })
 
-    return checkoutToCart(data.checkoutLineItemsAdd)
+    return checkoutToCart(checkoutLineItemsAdd)
   },
   useHook() {
     const { mutate } = useCart()
diff --git a/framework/shopify/cart/utils/checkout-to-cart.ts b/framework/shopify/cart/utils/checkout-to-cart.ts
index 104240220..42d797652 100644
--- a/framework/shopify/cart/utils/checkout-to-cart.ts
+++ b/framework/shopify/cart/utils/checkout-to-cart.ts
@@ -1,14 +1,26 @@
 import { Cart } from '@commerce/types'
-import { ValidationError } from '@commerce/utils/errors'
-import { normalizeCart } from '@framework/utils/normalize'
-import { Checkout, UserError } from '@framework/schema'
+import { CommerceError, ValidationError } from '@commerce/utils/errors'
 
-const checkoutToCart = (checkoutResponse: {
-  checkout: Checkout
-  userErrors?: UserError[]
-}): Cart => {
-  const checkout = checkoutResponse?.checkout
-  const userErrors = checkoutResponse?.userErrors
+import {
+  CheckoutLineItemsAddPayload,
+  CheckoutLineItemsUpdatePayload,
+  Maybe,
+} from '@framework/schema'
+import { normalizeCart } from '@framework/utils'
+
+export type CheckoutPayload =
+  | CheckoutLineItemsAddPayload
+  | CheckoutLineItemsUpdatePayload
+
+const checkoutToCart = (checkoutPayload?: Maybe<CheckoutPayload>): Cart => {
+  if (!checkoutPayload || !checkoutPayload?.checkout) {
+    throw new CommerceError({
+      message: 'Invalid response from Shopify',
+    })
+  }
+
+  const checkout = checkoutPayload?.checkout
+  const userErrors = checkoutPayload?.userErrors
 
   if (userErrors && userErrors.length) {
     throw new ValidationError({
diff --git a/framework/shopify/types.ts b/framework/shopify/types.ts
index 7f207b0c7..6ebfdf01d 100644
--- a/framework/shopify/types.ts
+++ b/framework/shopify/types.ts
@@ -23,25 +23,24 @@ export type OptionSelections = {
   option_value: number | string
 }
 
-export interface CartItemBody extends Core.CartItemBody {
+export type CartItemBody = Core.CartItemBody & {
   productId: string // The product id is always required for BC
   optionSelections?: OptionSelections
 }
 
-export interface GetCartHandlerBody extends Core.GetCartHandlerBody {}
+type X = Core.CartItemBody extends CartItemBody ? any : never
+type Y = CartItemBody extends Core.CartItemBody ? any : never
 
-export interface AddCartItemBody extends Core.AddCartItemBody<CartItemBody> {}
+export type GetCartHandlerBody = Core.GetCartHandlerBody
 
-export interface AddCartItemHandlerBody
-  extends Core.AddCartItemHandlerBody<CartItemBody> {}
+export type AddCartItemBody = Core.AddCartItemBody<CartItemBody>
 
-export interface UpdateCartItemBody
-  extends Core.UpdateCartItemBody<CartItemBody> {}
+export type AddCartItemHandlerBody = Core.AddCartItemHandlerBody<CartItemBody>
 
-export interface UpdateCartItemHandlerBody
-  extends Core.UpdateCartItemHandlerBody<CartItemBody> {}
+export type UpdateCartItemBody = Core.UpdateCartItemBody<CartItemBody>
 
-export interface RemoveCartItemBody extends Core.RemoveCartItemBody {}
+export type UpdateCartItemHandlerBody = Core.UpdateCartItemHandlerBody<CartItemBody>
 
-export interface RemoveCartItemHandlerBody
-  extends Core.RemoveCartItemHandlerBody {}
+export type RemoveCartItemBody = Core.RemoveCartItemBody
+
+export type RemoveCartItemHandlerBody = Core.RemoveCartItemHandlerBody
diff --git a/framework/shopify/utils/normalize.ts b/framework/shopify/utils/normalize.ts
index edd295ddd..79074bf24 100644
--- a/framework/shopify/utils/normalize.ts
+++ b/framework/shopify/utils/normalize.ts
@@ -81,20 +81,20 @@ export function normalizeProduct(productNode: ShopifyProduct): any {
   }
 }
 
-export function normalizeCart(data: Checkout): Cart {
+export function normalizeCart(checkout: Checkout): Cart {
   return {
-    id: data.id,
+    id: checkout.id,
     customerId: '',
     email: '',
-    createdAt: data.createdAt,
+    createdAt: checkout.createdAt,
     currency: {
-      code: data.currencyCode,
+      code: checkout.currencyCode,
     },
-    taxesIncluded: data.taxesIncluded,
-    lineItems: data.lineItems?.edges.map(normalizeLineItem),
-    lineItemsSubtotalPrice: data.subtotalPrice,
-    subtotalPrice: data.subtotalPrice,
-    totalPrice: data.totalPrice,
+    taxesIncluded: checkout.taxesIncluded,
+    lineItems: checkout.lineItems?.edges.map(normalizeLineItem),
+    lineItemsSubtotalPrice: checkout.subtotalPrice,
+    subtotalPrice: checkout.subtotalPrice,
+    totalPrice: checkout.totalPrice,
     discounts: [],
   }
 }