diff --git a/src/lib/server/shopping/repository.ts b/src/lib/server/shopping/repository.ts
index 5463f6c..2a40528 100644
--- a/src/lib/server/shopping/repository.ts
+++ b/src/lib/server/shopping/repository.ts
@@ -107,12 +107,22 @@ export function listShoppingList(
 }
 
 export function toggleCheck(
-  _db: Database.Database,
-  _nameKey: string,
-  _unitKey: string,
-  _checked: boolean
+  db: Database.Database,
+  nameKey: string,
+  unitKey: string,
+  checked: boolean
 ): void {
-  throw new Error('not implemented');
+  if (checked) {
+    db.prepare(
+      `INSERT INTO shopping_cart_check (name_key, unit_key)
+       VALUES (?, ?)
+       ON CONFLICT(name_key, unit_key) DO NOTHING`
+    ).run(nameKey, unitKey);
+  } else {
+    db.prepare(
+      'DELETE FROM shopping_cart_check WHERE name_key = ? AND unit_key = ?'
+    ).run(nameKey, unitKey);
+  }
 }
 
 export function clearCheckedItems(_db: Database.Database): void {
diff --git a/tests/integration/shopping-repository.test.ts b/tests/integration/shopping-repository.test.ts
index 437b087..8453e5f 100644
--- a/tests/integration/shopping-repository.test.ts
+++ b/tests/integration/shopping-repository.test.ts
@@ -5,7 +5,8 @@ import {
   addRecipeToCart,
   removeRecipeFromCart,
   listShoppingList,
-  setCartServings
+  setCartServings,
+  toggleCheck
 } from '../../src/lib/server/shopping/repository';
 import type { Recipe } from '../../src/lib/types';
 
@@ -185,3 +186,48 @@ describe('listShoppingList aggregation', () => {
     expect(rows[0].total_quantity).toBeNull();
   });
 });
+
+describe('toggleCheck', () => {
+  function setupOneRowCart() {
+    const db = openInMemoryForTest();
+    const id = insertRecipe(db, recipe({
+      ingredients: [{ position: 1, quantity: 200, unit: 'g', name: 'Mehl', note: null, raw_text: '', section_heading: null }]
+    }));
+    addRecipeToCart(db, id, null);
+    return { db, id };
+  }
+
+  it('marks a row as checked', () => {
+    const { db } = setupOneRowCart();
+    toggleCheck(db, 'mehl', 'g', true);
+    const rows = listShoppingList(db).rows;
+    expect(rows[0].checked).toBe(1);
+  });
+
+  it('unchecks a row when passed false', () => {
+    const { db } = setupOneRowCart();
+    toggleCheck(db, 'mehl', 'g', true);
+    toggleCheck(db, 'mehl', 'g', false);
+    expect(listShoppingList(db).rows[0].checked).toBe(0);
+  });
+
+  it('check survives removal of one recipe when another still contributes', () => {
+    const db = openInMemoryForTest();
+    const a = insertRecipe(db, recipe({
+      title: 'A',
+      ingredients: [{ position: 1, quantity: 100, unit: 'g', name: 'Mehl', note: null, raw_text: '', section_heading: null }]
+    }));
+    const b = insertRecipe(db, recipe({
+      title: 'B',
+      ingredients: [{ position: 1, quantity: 200, unit: 'g', name: 'Mehl', note: null, raw_text: '', section_heading: null }]
+    }));
+    addRecipeToCart(db, a, null);
+    addRecipeToCart(db, b, null);
+    toggleCheck(db, 'mehl', 'g', true);
+    // Rezept A weg, Mehl kommt noch aus B — check bleibt, mit neuer Menge
+    removeRecipeFromCart(db, a);
+    const rows = listShoppingList(db).rows;
+    expect(rows[0].checked).toBe(1);
+    expect(rows[0].total_quantity).toBe(200);
+  });
+});