diff --git a/projects/ngx-filesize/src/lib/filesize.pipe.ts b/projects/ngx-filesize/src/lib/filesize.pipe.ts
index 180416d2..d3749627 100644
--- a/projects/ngx-filesize/src/lib/filesize.pipe.ts
+++ b/projects/ngx-filesize/src/lib/filesize.pipe.ts
@@ -10,6 +10,8 @@ export class FileSizePipe implements PipeTransform {
     return filesize(value, options);
   }
 
+  transform(value: number, options?: any): string;
+  transform(value: number[], options?: any): string[];
   transform(value: number | number[], options?: any) {
     if (Array.isArray(value)) {
       return value.map(val => FileSizePipe.transformOne(val, options));