diff --git a/backend/src/clusters/entities/cluster-allocation-log.entity.ts b/backend/src/clusters/entities/cluster-allocation-log.entity.ts
index b091d4b..cfc0a50 100644
--- a/backend/src/clusters/entities/cluster-allocation-log.entity.ts
+++ b/backend/src/clusters/entities/cluster-allocation-log.entity.ts
@@ -17,7 +17,9 @@ export class ClusterAllocationLog {
   @PrimaryGeneratedColumn('uuid')
   id: string;
 
-  @Column({ nullable: true })
+  // Explicit `type` required: `string | null` reflects as Object and crashes
+  // TypeORM at metadata build (DataTypeNotSupportedError).
+  @Column({ type: 'uuid', nullable: true })
   applicationId?: string | null;
 
   @ManyToOne(() => Application, { nullable: true, onDelete: 'SET NULL' })
@@ -27,14 +29,14 @@ export class ClusterAllocationLog {
   @Column()
   userId: string;
 
-  @Column({ nullable: true })
+  @Column({ type: 'uuid', nullable: true })
   poolId?: string | null;
 
   @ManyToOne(() => ClusterPool, { nullable: true, onDelete: 'SET NULL' })
   @JoinColumn({ name: 'poolId' })
   pool: ClusterPool;
 
-  @Column({ nullable: true })
+  @Column({ type: 'uuid', nullable: true })
   selectedClusterId?: string | null;
 
   @ManyToOne(() => Cluster, { nullable: true, onDelete: 'SET NULL' })
diff --git a/backend/src/users/entities/user.entity.ts b/backend/src/users/entities/user.entity.ts
index 87164d0..53cd306 100644
--- a/backend/src/users/entities/user.entity.ts
+++ b/backend/src/users/entities/user.entity.ts
@@ -18,10 +18,13 @@ export class User {
   // optional contact field only — it is never used to authenticate.
   // Both are unique; Postgres treats NULLs as distinct, so accounts missing
   // either coexist freely.
-  @Column({ unique: true, nullable: true })
+  // NOTE: nullable string columns MUST declare an explicit `type` — TypeScript
+  // reflects the `string | null` union as `Object`, which TypeORM rejects with
+  // DataTypeNotSupportedError and crashes the backend at metadata build.
+  @Column({ type: 'varchar', unique: true, nullable: true })
   phone: string | null; // canonical E.164, e.g. +989121234567
 
-  @Column({ unique: true, nullable: true })
+  @Column({ type: 'varchar', unique: true, nullable: true })
   email: string | null;
 
   @Column({ default: false })