diff --git a/lib/services/entity-sync.ts b/lib/services/entity-sync.ts
index bb57f3b..744d0a7 100644
--- a/lib/services/entity-sync.ts
+++ b/lib/services/entity-sync.ts
@@ -255,10 +255,35 @@ export class EntitySyncService {
         }
       }
 
+      // Validate company_id foreign keys for tickets (defensive — Task 1 widening
+      // the Companies filter should make this a near-zero count, but catches the
+      // truly hard-deleted Autotask company case).
+      if (entity === EntityType.TICKETS) {
+        const validCompanyIds = await this.getValidCompanyIds();
+        let nullifiedCompanyCount = 0;
+        const nullifiedCompanySamples: number[] = [];
+        mappedRecords = mappedRecords.map(ticket => {
+          if (ticket.company_id && !validCompanyIds.has(ticket.company_id)) {
+            if (nullifiedCompanySamples.length < 5) {
+              nullifiedCompanySamples.push(ticket.id);
+            }
+            ticket.company_id = null;
+            nullifiedCompanyCount++;
+          }
+          return ticket;
+        });
+        if (nullifiedCompanyCount > 0) {
+          entityLogger.warn('Nullified ticket company_id for companies missing from mirror', {
+            nullifiedCount: nullifiedCompanyCount,
+            sampleTicketIds: nullifiedCompanySamples,
+          });
+        }
+      }
+
       // Validate resource foreign keys for tickets
       if (entity === EntityType.TICKETS) {
         const initialCount = mappedRecords.length;
-        
+
         // Get all valid resource IDs from database
         const validResourceIds = await this.getValidResourceIds();
         
@@ -721,6 +746,17 @@ export class EntitySyncService {
     return new Set(result.rows.map(row => Number(row.id)));
   }
 
+  /**
+   * Get all valid company IDs from the database
+   * Used to validate foreign key references before insert
+   * @returns Set of valid company IDs
+   */
+  private async getValidCompanyIds(): Promise<Set<number>> {
+    const query = 'SELECT id FROM companies WHERE is_deleted = false';
+    const result = await postgresClient.query<{ id: number }>(query);
+    return new Set(result.rows.map(row => Number(row.id)));
+  }
+
   /**
    * Used to validate foreign key references before insert
    * @returns Set of valid contact IDs