diff --git a/.changeset/fix-calculatedPriceSet-guard.md b/.changeset/fix-calculatedPriceSet-guard.md
new file mode 100644
index 0000000000000..5a2c9e241b508
--- /dev/null
+++ b/.changeset/fix-calculatedPriceSet-guard.md
@@ -0,0 +1,5 @@
+---
+"@medusajs/core-flows": patch
+---
+
+Return an invalid data error when adding a cart line item for a variant without a price
diff --git a/packages/core/core-flows/src/cart/workflows/__tests__/get-variants-and-items-with-prices.spec.ts b/packages/core/core-flows/src/cart/workflows/__tests__/get-variants-and-items-with-prices.spec.ts
new file mode 100644
index 0000000000000..263c65f11a9fa
--- /dev/null
+++ b/packages/core/core-flows/src/cart/workflows/__tests__/get-variants-and-items-with-prices.spec.ts
@@ -0,0 +1,41 @@
+import { createContainer } from "@medusajs/framework/awilix"
+import { MedusaError, ProductStatus } from "@medusajs/framework/utils"
+import {
+  createWorkflow,
+  WorkflowResponse,
+} from "@medusajs/framework/workflows-sdk"
+import { prepareVariantsAndItemsWithPricesStep } from "../get-variants-and-items-with-prices"
+
+describe("prepareVariantsAndItemsWithPricesStep", () => {
+  it("throws an invalid data error when a variant does not have a price", async () => {
+    const workflow = createWorkflow(
+      "test-prepare-variant-without-price",
+      () => {
+        const result = prepareVariantsAndItemsWithPricesStep({
+          cart: { id: "cart_1" },
+          items: [{ variant_id: "variant_1", quantity: 1 }],
+          variantsData: [
+            {
+              id: "variant_1",
+              product: {
+                id: "product_1",
+                status: ProductStatus.PUBLISHED,
+              },
+              inventory_items: [],
+            },
+          ],
+          calculatedPriceSets: {},
+        })
+
+        return new WorkflowResponse(result)
+      }
+    )
+
+    const execution = workflow(createContainer()).run()
+
+    await expect(execution).rejects.toMatchObject({
+      type: MedusaError.Types.INVALID_DATA,
+      message: "Variants with IDs variant_1 do not have a price",
+    })
+  })
+})
diff --git a/packages/core/core-flows/src/cart/workflows/get-variants-and-items-with-prices.ts b/packages/core/core-flows/src/cart/workflows/get-variants-and-items-with-prices.ts
index 149a629d5d91e..520dc81910a14 100644
--- a/packages/core/core-flows/src/cart/workflows/get-variants-and-items-with-prices.ts
+++ b/packages/core/core-flows/src/cart/workflows/get-variants-and-items-with-prices.ts
@@ -135,7 +135,7 @@ export const prepareVariantsAndItemsWithPricesStep = createStep(
         isCustomPrice: isCustomPrice,
       }
 
-      if (variant && !isCustomPrice) {
+      if (variant && !isCustomPrice && calculatedPriceSet) {
         input.unitPrice = calculatedPriceSet.calculated_amount
         input.isTaxInclusive =
           calculatedPriceSet.is_calculated_price_tax_inclusive