diff --git a/backend/src/modules/projects/projects.service.ts b/backend/src/modules/projects/projects.service.ts
index 11a9faf..77914cb 100644
--- a/backend/src/modules/projects/projects.service.ts
+++ b/backend/src/modules/projects/projects.service.ts
@@ -157,6 +157,9 @@ export class ProjectsService {
     const params: any[] = [];
     let idx = 1;
 
+    // Date columns must be null (not empty string) for PostgreSQL DATE type
+    const dateFields = new Set(['last_replacement_date', 'next_replacement_date', 'planned_date']);
+
     // Build dynamic SET clause
     const fields: [string, string][] = [
       ['name', 'name'], ['description', 'description'], ['category', 'category'],
@@ -175,7 +178,8 @@ export class ProjectsService {
     for (const [dtoKey, dbCol] of fields) {
       if (dto[dtoKey] !== undefined) {
         sets.push(`${dbCol} = $${idx++}`);
-        params.push(dto[dtoKey]);
+        const val = dateFields.has(dtoKey) && dto[dtoKey] === '' ? null : dto[dtoKey];
+        params.push(val);
       }
     }
 
@@ -276,7 +280,7 @@ export class ProjectsService {
     await this.findOne(id);
     const rows = await this.tenant.query(
       'UPDATE projects SET planned_date = $2, updated_at = NOW() WHERE id = $1 RETURNING *',
-      [id, planned_date],
+      [id, planned_date || null],
     );
     return rows[0];
   }