diff --git a/API.articleproperty.md b/API.articleproperty.md
index 684142b..c0161d2 100644
--- a/API.articleproperty.md
+++ b/API.articleproperty.md
@@ -37,13 +37,13 @@ Lists the properties of an article by its SKU.
 
 **Returns**
 
-`Promise<Array<{id: number, articleId: number, propertyId: number, name: string, value: string, sort: number}>>`
+`Promise<Array<{id: number, articleId: number, propertyId: number, name: string, exclusive: boolean, value: string, sort: number}>>`
 
 ## `articleproperty.setByArticleSku`
 
 *Source: `src/store/articleproperty/setByArticleSku.js`*
 
-Replaces all properties for an article by its SKU.
+Replaces all properties for an article by its SKU. Enforces exclusive flag on property names.
 
 **Parameters**
 
@@ -56,4 +56,4 @@ Replaces all properties for an article by its SKU.
 
 **Returns**
 
-`Promise<Array<{id: number, articleId: number, propertyId: number, name: string, value: string, sort: number}>>`
+`Promise<Array<{id: number, articleId: number, propertyId: number, name: string, exclusive: boolean, value: string, sort: number}>>`
diff --git a/API.md b/API.md
index 4dc071b..2bd25b6 100644
--- a/API.md
+++ b/API.md
@@ -222,8 +222,8 @@ The store is exposed as a `LibDashStore` instance (see `src/index.js`). Each met
   - `setByArticleSku(googleAuthId: number, sku: string, values: Array<number|{attributeValueId: number, sort?: number}>, tx?: object): Promise<Array<{id: number, articleId: number, attributeId: number, attributeName: string, exclusive: boolean, attributeValueId: number, value: string, sort: number}>>`
 - [articleproperty](API.articleproperty.md)
   - `delete(googleAuthId: number, sku: string, propertyId: number, tx?: object): Promise<void>`
-  - `listByArticleSku(googleAuthId: number, sku: string, tx?: object): Promise<Array<{id: number, articleId: number, propertyId: number, name: string, value: string, sort: number}>>`
-  - `setByArticleSku(googleAuthId: number, sku: string, properties: Array<{propertyId: number, value: string, sort?: number}>, tx?: object): Promise<Array<{id: number, articleId: number, propertyId: number, name: string, value: string, sort: number}>>`
+  - `listByArticleSku(googleAuthId: number, sku: string, tx?: object): Promise<Array<{id: number, articleId: number, propertyId: number, name: string, exclusive: boolean, value: string, sort: number}>>`
+  - `setByArticleSku(googleAuthId: number, sku: string, properties: Array<{propertyId: number, value: string, sort?: number}>, tx?: object): Promise<Array<{id: number, articleId: number, propertyId: number, name: string, exclusive: boolean, value: string, sort: number}>>`
 - [attributename](API.attributename.md)
   - `create(googleAuthId: number, input: {name: string, sort?: number, exclusive?: boolean}, tx?: object): Promise<{id: number, name: string, sort: number, exclusive: boolean, values: Array}>`
   - `delete(googleAuthId: number, id: number, tx?: object): Promise<void>`
@@ -243,10 +243,10 @@ The store is exposed as a `LibDashStore` instance (see `src/index.js`). Each met
   - `list(googleAuthId: number, tx?: object): Promise<Array<{id: number, company_id: number, name: string, width: number, height: number, dpi: number, type: string, content: object, thumb: Buffer|null}>>`
   - `update(googleAuthId: number, id: number, input: {name?: string, width?: number, height?: number, dpi?: number, type?: string, content?: object, thumb?: Buffer|null}, tx?: object): Promise<{id: number, company_id: number, name: string, width: number, height: number, dpi: number, type: string, content: object, thumb: Buffer|null}>`
 - [propertyname](API.propertyname.md)
-  - `create(googleAuthId: number, input: {name: string, sort?: number}, tx?: object): Promise<{id: number, name: string, sort: number}>`
+  - `create(googleAuthId: number, input: {name: string, sort?: number, exclusive?: boolean}, tx?: object): Promise<{id: number, name: string, sort: number, exclusive: boolean}>`
   - `delete(googleAuthId: number, id: number, tx?: object): Promise<void>`
-  - `list(googleAuthId: number, tx?: object): Promise<Array<{id: number, name: string, sort: number}>>`
+  - `list(googleAuthId: number, tx?: object): Promise<Array<{id: number, name: string, sort: number, exclusive: boolean}>>`
   - `order(googleAuthId: number, input: {propertynameIds: Array<number>}, tx?: object): Promise<{propertynameIds: Array<number>}>`
-  - `update(googleAuthId: number, id: number, input: {name?: string, sort?: number}, tx?: object): Promise<{id: number, name: string, sort: number}>`
+  - `update(googleAuthId: number, id: number, input: {name?: string, sort?: number, exclusive?: boolean}, tx?: object): Promise<{id: number, name: string, sort: number, exclusive: boolean}>`
 - [runner.js](API.runner.js.md)
   - `runner(provider: import('../providers/provider.js').DatabaseProvider, tx?: object): ((sql: string, params?: object) => Promise<import('../providers/provider.js').QueryResult>) & { query: Function, dialect?: string }`
diff --git a/API.propertyname.md b/API.propertyname.md
index a663c2b..2235771 100644
--- a/API.propertyname.md
+++ b/API.propertyname.md
@@ -16,11 +16,12 @@ Creates a property name for the user's selected company.
 | `input` | `object` | The property name input. |
 | `input.name` | `string` | The property name. |
 | `[input.sort]` | `number` | Optional sort order. |
+| `[input.exclusive=false]` | `boolean` | Whether values are mutually exclusive on an article. |
 | `[tx]` | `object` | Optional transaction. |
 
 **Returns**
 
-`Promise<{id: number, name: string, sort: number}>`
+`Promise<{id: number, name: string, sort: number, exclusive: boolean}>`
 
 ## `propertyname.delete`
 
@@ -55,7 +56,7 @@ Lists the property names for the user's selected company.
 
 **Returns**
 
-`Promise<Array<{id: number, name: string, sort: number}>>`
+`Promise<Array<{id: number, name: string, sort: number, exclusive: boolean}>>`
 
 ## `propertyname.order`
 
@@ -91,8 +92,9 @@ Updates a property name for the user's selected company.
 | `input` | `object` | Update patch. |
 | `[input.name]` | `string` | New name. |
 | `[input.sort]` | `number` | New sort. |
+| `[input.exclusive]` | `boolean` | New exclusive flag. |
 | `[tx]` | `object` | Optional transaction. |
 
 **Returns**
 
-`Promise<{id: number, name: string, sort: number}>`
+`Promise<{id: number, name: string, sort: number, exclusive: boolean}>`
diff --git a/src/providers/mssql/index.js b/src/providers/mssql/index.js
index 3722cde..d899d7e 100644
--- a/src/providers/mssql/index.js
+++ b/src/providers/mssql/index.js
@@ -177,6 +177,11 @@ export class MssqlProvider {
         BEGIN
             ALTER TABLE posterminal ADD clientserial NVARCHAR(255) NULL;
         END
+
+        IF OBJECT_ID(N'dbo.propertyname', N'U') IS NOT NULL AND COL_LENGTH('propertyname', 'exclusive') IS NULL
+        BEGIN
+            ALTER TABLE propertyname ADD exclusive BIT NOT NULL CONSTRAINT DF_propertyname_exclusive DEFAULT 0;
+        END
       `);
     } catch {
       // ignore
diff --git a/src/providers/mssql/queries/articleproperty.js b/src/providers/mssql/queries/articleproperty.js
index cdcd456..0cf4526 100644
--- a/src/providers/mssql/queries/articleproperty.js
+++ b/src/providers/mssql/queries/articleproperty.js
@@ -4,6 +4,7 @@ SELECT
     ap.article_id AS articleId,
     ap.property_id AS propertyId,
     pn.name AS name,
+    pn.exclusive,
     ap.value,
     ap.sort
 FROM articleproperty ap
diff --git a/src/providers/mssql/queries/propertyname.js b/src/providers/mssql/queries/propertyname.js
index 4e63cdc..8ccd003 100644
--- a/src/providers/mssql/queries/propertyname.js
+++ b/src/providers/mssql/queries/propertyname.js
@@ -2,7 +2,8 @@ export const LIST_BY_COMPANY = `
 SELECT
     id,
     name,
-    sort
+    sort,
+    exclusive
 FROM propertyname
 WHERE company_id = @companyId
 ORDER BY sort ASC, id ASC
@@ -20,7 +21,8 @@ SELECT
     id,
     company_id,
     name,
-    sort
+    sort,
+    exclusive
 FROM propertyname
 WHERE id = @id AND company_id = @companyId
 `;
@@ -30,7 +32,8 @@ SELECT
     id,
     company_id,
     name,
-    sort
+    sort,
+    exclusive
 FROM propertyname
 WHERE name = @name AND company_id = @companyId
 `;
@@ -42,14 +45,14 @@ WHERE company_id = @companyId
 `;
 
 export const CREATE = `
-INSERT INTO propertyname (company_id, name, sort)
-OUTPUT INSERTED.id, INSERTED.name, INSERTED.sort
-VALUES (@companyId, @name, @sort)
+INSERT INTO propertyname (company_id, name, sort, exclusive)
+OUTPUT INSERTED.id, INSERTED.name, INSERTED.sort, INSERTED.exclusive
+VALUES (@companyId, @name, @sort, @exclusive)
 `;
 
 export const UPDATE_BY_ID = `
 UPDATE propertyname
-SET name = @name, sort = @sort
+SET name = @name, sort = @sort, exclusive = @exclusive
 WHERE id = @id AND company_id = @companyId
 `;
 
diff --git a/src/providers/mssql/schema.js b/src/providers/mssql/schema.js
index e5a7e49..d28ce86 100644
--- a/src/providers/mssql/schema.js
+++ b/src/providers/mssql/schema.js
@@ -902,6 +902,7 @@ BEGIN
         company_id INT NOT NULL,
         name NVARCHAR(255) NOT NULL,
         sort INT NOT NULL CONSTRAINT DF_propertyname_sort DEFAULT 0,
+        exclusive BIT NOT NULL CONSTRAINT DF_propertyname_exclusive DEFAULT 0,
         CONSTRAINT FK_propertyname_company FOREIGN KEY (company_id) REFERENCES company(id) ON DELETE CASCADE,
         CONSTRAINT UQ_propertyname_company_name UNIQUE (company_id, name)
     );
@@ -918,8 +919,7 @@ BEGIN
         value NVARCHAR(MAX) NOT NULL,
         sort INT NOT NULL CONSTRAINT DF_articleproperty_sort DEFAULT 0,
         CONSTRAINT FK_articleproperty_article FOREIGN KEY (article_id) REFERENCES article(id) ON DELETE CASCADE,
-        CONSTRAINT FK_articleproperty_property FOREIGN KEY (property_id) REFERENCES propertyname(id) ON DELETE CASCADE,
-        CONSTRAINT UQ_articleproperty_article_property UNIQUE (article_id, property_id)
+        CONSTRAINT FK_articleproperty_property FOREIGN KEY (property_id) REFERENCES propertyname(id) ON DELETE CASCADE
     );
 END
 `;
diff --git a/src/providers/sqlite3/index.js b/src/providers/sqlite3/index.js
index fa922c4..86ce7c9 100644
--- a/src/providers/sqlite3/index.js
+++ b/src/providers/sqlite3/index.js
@@ -421,6 +421,11 @@ export class BetterSqlite3Provider extends BetterSqlite3Executor {
       if (posterminalCols.length > 0 && !posterminalCols.includes('clientserial')) {
         this.db.exec(`ALTER TABLE posterminal ADD COLUMN clientserial TEXT`);
       }
+
+      const propertynameCols = this.db.pragma('table_info("propertyname")').map((c) => c.name);
+      if (propertynameCols.length > 0 && !propertynameCols.includes('exclusive')) {
+        this.db.exec(`ALTER TABLE propertyname ADD COLUMN exclusive INTEGER NOT NULL DEFAULT 0`);
+      }
     } catch {
       // ignore
     }
diff --git a/src/providers/sqlite3/schema.js b/src/providers/sqlite3/schema.js
index ccf0079..a029849 100644
--- a/src/providers/sqlite3/schema.js
+++ b/src/providers/sqlite3/schema.js
@@ -627,6 +627,7 @@ CREATE TABLE IF NOT EXISTS propertyname (
     company_id INTEGER NOT NULL,
     name TEXT NOT NULL,
     sort INTEGER NOT NULL DEFAULT 0,
+    exclusive INTEGER NOT NULL DEFAULT 0,
     FOREIGN KEY (company_id) REFERENCES company(id) ON DELETE CASCADE,
     UNIQUE (company_id, name)
 );
@@ -640,8 +641,7 @@ CREATE TABLE IF NOT EXISTS articleproperty (
     value TEXT NOT NULL,
     sort INTEGER NOT NULL DEFAULT 0,
     FOREIGN KEY (article_id) REFERENCES article(id) ON DELETE CASCADE,
-    FOREIGN KEY (property_id) REFERENCES propertyname(id) ON DELETE CASCADE,
-    UNIQUE (article_id, property_id)
+    FOREIGN KEY (property_id) REFERENCES propertyname(id) ON DELETE CASCADE
 );
 `;
 
diff --git a/src/store/articleproperty/listByArticleSku.js b/src/store/articleproperty/listByArticleSku.js
index fbf91bf..89525d0 100644
--- a/src/store/articleproperty/listByArticleSku.js
+++ b/src/store/articleproperty/listByArticleSku.js
@@ -13,7 +13,7 @@ export default function listByArticleSku(provider) {
    * @param {number} googleAuthId - The id of the Google auth user.
    * @param {string} sku - The article SKU.
    * @param {object} [tx] - Optional transaction.
-   * @returns {Promise<Array<{id: number, articleId: number, propertyId: number, name: string, value: string, sort: number}>>}
+   * @returns {Promise<Array<{id: number, articleId: number, propertyId: number, name: string, exclusive: boolean, value: string, sort: number}>>}
    */
   return async (googleAuthId, sku, tx) => {
     const runner = makeRunner(provider, tx);
@@ -25,6 +25,7 @@ export default function listByArticleSku(provider) {
       articleId: row.articleId,
       propertyId: row.propertyId,
       name: row.name,
+      exclusive: Boolean(row.exclusive),
       value: row.value,
       sort: row.sort,
     }));
diff --git a/src/store/articleproperty/setByArticleSku.js b/src/store/articleproperty/setByArticleSku.js
index cc18c41..8d21df4 100644
--- a/src/store/articleproperty/setByArticleSku.js
+++ b/src/store/articleproperty/setByArticleSku.js
@@ -24,12 +24,13 @@ export default function setByArticleSku(provider) {
 
   /**
    * Replaces all properties for an article by its SKU.
+   * Enforces exclusive flag on property names.
    *
    * @param {number} googleAuthId - The id of the Google auth user.
    * @param {string} sku - The article SKU.
    * @param {Array<{propertyId: number, value: string, sort?: number}>} properties - The properties to set.
    * @param {object} [tx] - Optional transaction.
-   * @returns {Promise<Array<{id: number, articleId: number, propertyId: number, name: string, value: string, sort: number}>>}
+   * @returns {Promise<Array<{id: number, articleId: number, propertyId: number, name: string, exclusive: boolean, value: string, sort: number}>>}
    */
   return async (googleAuthId, sku, properties = [], tx) => {
     if (!Array.isArray(properties)) {
@@ -40,7 +41,7 @@ export default function setByArticleSku(provider) {
       const { articleId, companyId } = await resolve(googleAuthId, sku, runner);
 
       const validated = [];
-      const seenProps = new Set();
+      const seenExclusiveProps = new Set();
 
       for (let i = 0; i < properties.length; i++) {
         const item = properties[i];
@@ -48,21 +49,27 @@ export default function setByArticleSku(provider) {
         if (!Number.isInteger(propertyId) || propertyId <= 0) {
           throw new Error('Invalid propertyId');
         }
-        if (seenProps.has(propertyId)) {
-          throw new Error('Duplicate propertyId');
-        }
-        seenProps.add(propertyId);
 
         const propRes = await runner.query(getPropSql, { id: propertyId, companyId });
-        if (!propRes.rows[0]) {
+        const prop = propRes.rows[0];
+        if (!prop) {
           throw new Error(`Property not found: ${propertyId}`);
         }
 
+        const isExclusive = Boolean(prop.exclusive);
+        if (isExclusive) {
+          if (seenExclusiveProps.has(propertyId)) {
+            throw new Error(`Property "${prop.name}" is exclusive and can only have one value`);
+          }
+          seenExclusiveProps.add(propertyId);
+        }
+
         const value = item.value != null ? String(item.value).trim() : '';
         const sort = item.sort != null && Number.isInteger(item.sort) ? item.sort : i;
         validated.push({
           propertyId,
-          name: propRes.rows[0].name,
+          name: prop.name,
+          exclusive: isExclusive,
           value,
           sort,
         });
@@ -84,6 +91,7 @@ export default function setByArticleSku(provider) {
           articleId,
           propertyId: item.propertyId,
           name: item.name,
+          exclusive: item.exclusive,
           value: item.value,
           sort: item.sort,
         });
diff --git a/src/store/propertyname/create.js b/src/store/propertyname/create.js
index c33e551..62c10c3 100644
--- a/src/store/propertyname/create.js
+++ b/src/store/propertyname/create.js
@@ -22,8 +22,9 @@ export default function create(provider) {
    * @param {object} input - The property name input.
    * @param {string} input.name - The property name.
    * @param {number} [input.sort] - Optional sort order.
+   * @param {boolean} [input.exclusive=false] - Whether values are mutually exclusive on an article.
    * @param {object} [tx] - Optional transaction.
-   * @returns {Promise<{id: number, name: string, sort: number}>}
+   * @returns {Promise<{id: number, name: string, sort: number, exclusive: boolean}>}
    */
   return async (googleAuthId, input = {}, tx) => {
     const name = input.name?.trim();
@@ -40,13 +41,16 @@ export default function create(provider) {
       sort = next.rows[0].sort;
     }
 
+    const exclusive = Boolean(input.exclusive) ? 1 : 0;
+
     const result = await runner.query(createSql, {
       companyId,
       name,
       sort,
+      exclusive,
     });
 
     const id = result.rows[0]?.id ?? result.insertId;
-    return { id, name, sort };
+    return { id, name, sort, exclusive: Boolean(exclusive) };
   };
 }
diff --git a/src/store/propertyname/list.js b/src/store/propertyname/list.js
index f09f95f..1496719 100644
--- a/src/store/propertyname/list.js
+++ b/src/store/propertyname/list.js
@@ -12,7 +12,7 @@ export default function list(provider) {
    *
    * @param {number} googleAuthId - The id of the Google auth user.
    * @param {object} [tx] - Optional transaction.
-   * @returns {Promise<Array<{id: number, name: string, sort: number}>>}
+   * @returns {Promise<Array<{id: number, name: string, sort: number, exclusive: boolean}>>}
    */
   return async (googleAuthId, tx) => {
     const { companyId } = await access(googleAuthId, tx);
@@ -21,6 +21,7 @@ export default function list(provider) {
       id: row.id,
       name: row.name,
       sort: row.sort,
+      exclusive: Boolean(row.exclusive),
     }));
   };
 }
diff --git a/src/store/propertyname/update.js b/src/store/propertyname/update.js
index 5403c30..76082ae 100644
--- a/src/store/propertyname/update.js
+++ b/src/store/propertyname/update.js
@@ -23,8 +23,9 @@ export default function update(provider) {
    * @param {object} input - Update patch.
    * @param {string} [input.name] - New name.
    * @param {number} [input.sort] - New sort.
+   * @param {boolean} [input.exclusive] - New exclusive flag.
    * @param {object} [tx] - Optional transaction.
-   * @returns {Promise<{id: number, name: string, sort: number}>}
+   * @returns {Promise<{id: number, name: string, sort: number, exclusive: boolean}>}
    */
   return async (googleAuthId, id, input = {}, tx) => {
     if (!id || !Number.isInteger(Number(id))) {
@@ -44,14 +45,16 @@ export default function update(provider) {
       throw new Error('Name required');
     }
     const sort = input.sort !== undefined && Number.isInteger(input.sort) ? input.sort : existing.rows[0].sort;
+    const exclusive = input.exclusive !== undefined ? (Boolean(input.exclusive) ? 1 : 0) : existing.rows[0].exclusive;
 
     await runner.query(updateSql, {
       id,
       companyId,
       name,
       sort,
+      exclusive,
     });
 
-    return { id, name, sort };
+    return { id, name, sort, exclusive: Boolean(exclusive) };
   };
 }