diff --git a/management/src/components/TenantModal.jsx b/management/src/components/TenantModal.jsx
index 5b73e49..3d86853 100644
--- a/management/src/components/TenantModal.jsx
+++ b/management/src/components/TenantModal.jsx
@@ -130,7 +130,8 @@ const TenantModal = ({ isOpen, onClose, tenant = null, onSave }) => {
       const tenantData = {
         ...formData,
         auth_config: cleanAuthConfig,
-        // Convert empty email strings to null to avoid validation errors
+        // Convert empty strings to null to avoid validation errors
+        domain: formData.domain?.trim() || null,
         admin_email: formData.admin_email?.trim() || null,
         billing_email: formData.billing_email?.trim() || null
       }
diff --git a/server/routes/management.js b/server/routes/management.js
index 8f71ff3..1346b05 100644
--- a/server/routes/management.js
+++ b/server/routes/management.js
@@ -218,6 +218,11 @@ router.post('/tenants', async (req, res) => {
       });
     }
 
+    // Convert empty domain string to null to avoid unique constraint issues
+    if (tenantData.domain === '') {
+      tenantData.domain = null;
+    }
+
     // Check for unique slug
     const existingTenant = await Tenant.findOne({ where: { slug: tenantData.slug } });
     if (existingTenant) {
@@ -227,6 +232,17 @@ router.post('/tenants', async (req, res) => {
       });
     }
 
+    // Check for unique domain if provided
+    if (tenantData.domain) {
+      const existingDomain = await Tenant.findOne({ where: { domain: tenantData.domain } });
+      if (existingDomain) {
+        return res.status(409).json({
+          success: false,
+          message: 'Domain already exists for another tenant'
+        });
+      }
+    }
+
     // Log management action
     console.log(`Management: Admin ${req.managementUser.username} creating tenant: ${tenantData.name}`);
 
@@ -295,10 +311,33 @@ router.put('/tenants/:id', async (req, res) => {
       });
     }
 
+    const updateData = req.body;
+
+    // Convert empty domain string to null to avoid unique constraint issues
+    if (updateData.domain === '') {
+      updateData.domain = null;
+    }
+
+    // Check for unique domain if provided and different from current
+    if (updateData.domain && updateData.domain !== tenant.domain) {
+      const existingDomain = await Tenant.findOne({ 
+        where: { 
+          domain: updateData.domain,
+          id: { [require('sequelize').Op.ne]: tenant.id }
+        } 
+      });
+      if (existingDomain) {
+        return res.status(409).json({
+          success: false,
+          message: 'Domain already exists for another tenant'
+        });
+      }
+    }
+
     // Log management action
     console.log(`Management: Admin ${req.managementUser.username} updating tenant: ${tenant.name}`);
 
-    await tenant.update(req.body);
+    await tenant.update(updateData);
 
     res.json({
       success: true,