diff --git a/src/main/resources/static/js/multitool/PdfContainer.js b/src/main/resources/static/js/multitool/PdfContainer.js
index 907e099a..4c7c8497 100644
--- a/src/main/resources/static/js/multitool/PdfContainer.js
+++ b/src/main/resources/static/js/multitool/PdfContainer.js
@@ -240,7 +240,7 @@ class PdfContainer {
                 inputArr.pop(); // remove right part after last dot
             }
 
-            filenameInput.value = inputArr.join();
+            filenameInput.value = inputArr.join('');
             this.filename = filenameInput.value;
         }