diff --git a/order-routing/rust/pickup-point-delivery-option-generators/default/src/run.rs b/order-routing/rust/pickup-point-delivery-option-generators/default/src/run.rs
index 098a7689..88cbabee 100644
--- a/order-routing/rust/pickup-point-delivery-option-generators/default/src/run.rs
+++ b/order-routing/rust/pickup-point-delivery-option-generators/default/src/run.rs
@@ -138,7 +138,7 @@ fn build_business_hours(
         .map(|day| {
             let day_parts: Vec<&str> = day.as_str().unwrap().split(": ").collect();
             let day_name = serde_json::from_str::<run::output::Weekday>(
-                format!("\"{}\"", &day_parts[0].to_uppercase()).as_str(),
+                format!("\"{}\"", day_parts[0].to_uppercase()).as_str(),
             )
             .unwrap();
             if day_parts[1] == "Closed" {
diff --git a/sample-apps/update-line-item/extensions/update-line-item-js/src/run.js b/sample-apps/update-line-item/extensions/update-line-item-js/src/run.js
index 159d2a5a..d19d80d6 100644
--- a/sample-apps/update-line-item/extensions/update-line-item-js/src/run.js
+++ b/sample-apps/update-line-item/extensions/update-line-item-js/src/run.js
@@ -51,24 +51,35 @@ export function run(input) {
 function optionallyBuildUpdateOperation(
   { id: cartLineId, merchandise, cost, fabricLength }
 ) {
-  const hasFabricLength = fabricLength && Number(fabricLength.value) > 0;
+  if (merchandise.__typename !== "ProductVariant" || !fabricLength) {
+    return null;
+  }
 
-  if (
-    merchandise.__typename === "ProductVariant" &&
-    hasFabricLength
-  ) {
-    return {
-      cartLineId,
-      title: `${merchandise.title} (${fabricLength.value}m)`,
-      price: {
-        adjustment: {
-          fixedPricePerUnit: {
-            amount: (Number(fabricLength.value) * cost.amountPerQuantity.amount).toFixed(2)
-          }
-        }
-      }
-    };
+  // The fabric length is provided by the customer, so treat it as untrusted:
+  // only a positive, finite number is a valid length.
+  const length = Number(fabricLength.value);
+  if (!Number.isFinite(length) || length <= 0) {
+    return null;
+  }
+
+  const amount = (length * cost.amountPerQuantity.amount).toFixed(2);
+
+  // Rounding to cents happens after the multiplication, so a tiny positive
+  // length can still round the price down to "0.00". Never make the line free:
+  // leave it at its original price instead.
+  if (Number(amount) <= 0) {
+    return null;
   }
 
-  return null;
+  return {
+    cartLineId,
+    title: `${merchandise.title} (${fabricLength.value}m)`,
+    price: {
+      adjustment: {
+        fixedPricePerUnit: {
+          amount
+        }
+      }
+    }
+  };
 }
diff --git a/sample-apps/update-line-item/extensions/update-line-item-js/src/run.test.js b/sample-apps/update-line-item/extensions/update-line-item-js/src/run.test.js
index b889ce91..7fdb5711 100644
--- a/sample-apps/update-line-item/extensions/update-line-item-js/src/run.test.js
+++ b/sample-apps/update-line-item/extensions/update-line-item-js/src/run.test.js
@@ -81,4 +81,104 @@ describe("cart transform function", () => {
       ],
     });
   });
+
+  it("returns NO_CHANGES when the fabric length would round the price down to zero", () => {
+    expect(
+      run({
+        cart: {
+          lines: [
+            {
+              id: "1",
+              cost: {
+                amountPerQuantity: {
+                  amount: "10.0",
+                  currencyCode: "CAD"
+                }
+              },
+              fabricLength: {
+                value: "0.0001"
+              },
+              merchandise: {
+                __typename: "ProductVariant",
+                id: "gid://shopify/ProductVariant/2",
+                title: "Custom Fabric"
+              },
+            },
+          ],
+        },
+      })
+    ).toStrictEqual({ operations: [] });
+  });
+
+  it("returns NO_CHANGES when the fabric length is not a finite number", () => {
+    expect(
+      run({
+        cart: {
+          lines: [
+            {
+              id: "1",
+              cost: {
+                amountPerQuantity: {
+                  amount: "10.0",
+                  currencyCode: "CAD"
+                }
+              },
+              fabricLength: {
+                value: "Infinity"
+              },
+              merchandise: {
+                __typename: "ProductVariant",
+                id: "gid://shopify/ProductVariant/2",
+                title: "Custom Fabric"
+              },
+            },
+          ],
+        },
+      })
+    ).toStrictEqual({ operations: [] });
+  });
+
+  it("returns operations when the fabric length prices the line at the smallest chargeable amount", () => {
+    expect(
+      run({
+        cart: {
+          lines: [
+            {
+              id: "1",
+              cost: {
+                amountPerQuantity: {
+                  amount: "10.0",
+                  currencyCode: "CAD"
+                }
+              },
+              fabricLength: {
+                value: "0.001"
+              },
+              merchandise: {
+                __typename: "ProductVariant",
+                id: "gid://shopify/ProductVariant/2",
+                title: "Custom Fabric"
+              },
+            },
+          ],
+        },
+      })
+    ).toStrictEqual({
+      operations: [
+        {
+          update: {
+            cartLineId: "1",
+            title: "Custom Fabric (0.001m)",
+            price: {
+              adjustment: {
+                fixedPricePerUnit: {
+                  amount: "0.01"
+                }
+              }
+            }
+          },
+        },
+      ],
+    });
+  });
 });