diff --git a/docxtpl/__init__.py b/docxtpl/__init__.py
index 1cc6eca..0286f5f 100644
--- a/docxtpl/__init__.py
+++ b/docxtpl/__init__.py
@@ -463,6 +463,8 @@ class DocxTemplate(object):
                 DocxTemplate(docx_file).save(tmp_file)
                 tmp_file.seek(0)
                 docx_file.seek(0)
+                docx_file.truncate()
+                docx_file.seek(0)
 
             else:
                 tmp_file = '%s_docxtpl_before_replace_medias' % docx_file