diff --git a/docxtpl/template.py b/docxtpl/template.py
index 4467a09..cb8219d 100644
--- a/docxtpl/template.py
+++ b/docxtpl/template.py
@@ -6,7 +6,7 @@ Created : 2015-03-12
 """
 
 from os import PathLike
-from typing import Any, Optional, IO, Union, Dict
+from typing import Any, Optional, IO, Union, Dict, Set
 from .subdoc import Subdoc
 import functools
 import io
@@ -36,7 +36,7 @@ class DocxTemplate(object):
     HEADER_URI = "http://schemas.openxmlformats.org/officeDocument/2006/relationships/header"
     FOOTER_URI = "http://schemas.openxmlformats.org/officeDocument/2006/relationships/footer"
 
-    def __init__(self, template_file_or_path: Union[IO[bytes], str, PathLike[str]]):
+    def __init__(self, template_file_or_path: Union[IO[bytes], str, PathLike[str]]) -> None:
         self.template_file_or_path = template_file_or_path
         self.reset_replacements()
         self.docx = None
@@ -324,7 +324,7 @@ class DocxTemplate(object):
             new_part.load_rel(rel.reltype, rel._target, rel.rId, rel.is_external)
         self.docx._part._rels[relKey]._target = new_part
 
-    def render(self, context: Dict[str, Any], jinja_env: Optional[Environment]=None, autoescape: bool=False):
+    def render(self, context: Dict[str, Any], jinja_env: Optional[Environment]=None, autoescape: bool=False) -> None:
         # init template working attributes
         self.render_init()
 
@@ -722,7 +722,7 @@ class DocxTemplate(object):
         self.post_processing(output_file_or_path)
         self.is_saved = True
 
-    def get_undeclared_template_variables(self, jinja_env=None):
+    def get_undeclared_template_variables(self, jinja_env: Optional[Environment]=None) -> Set[str]:
         self.init_docx()
         xml = self.get_xml()
         xml = self.patch_xml(xml)