diff --git a/diff_edit/__init__.py b/diff_edit/__init__.py
index aea8e69..3e20247 100755
--- a/diff_edit/__init__.py
+++ b/diff_edit/__init__.py
@@ -165,7 +165,8 @@ class DiffEditor:
         with contextlib.suppress(AttributeError):
             del self.diff
 
-    def _highlight_lines(self, appearance, start, end, opcode, change_opcode):
+    @staticmethod
+    def _highlight_lines(appearance, start, end, opcode, change_opcode):
         if opcode == change_opcode:
             for index in range(start, end):
                 appearance[index] = highlight_str(appearance[index], (0, 200, 0), 0.6)
diff --git a/diff_edit/editor.py b/diff_edit/editor.py
index 8a4c6c7..918e525 100755
--- a/diff_edit/editor.py
+++ b/diff_edit/editor.py
@@ -118,8 +118,9 @@ class Text:
     def get_text(self):
         return "\n".join(self)
 
+    @staticmethod
     @functools.lru_cache(maxsize=5000)
-    def _convert_line(self, line, max_line_length):
+    def _convert_line(line, max_line_length):
         return expand_str(line).ljust(max_line_length)
 
     def appearance(self):