diff --git a/mitreattack/diffStix/changelog_helper.py b/mitreattack/diffStix/changelog_helper.py
index fe88b70..9eeff6b 100644
--- a/mitreattack/diffStix/changelog_helper.py
+++ b/mitreattack/diffStix/changelog_helper.py
@@ -2429,7 +2429,7 @@ def get_new_changelog_md(
     if markdown_file:
         logger.info("Writing markdown to file")
         Path(markdown_file).parent.mkdir(parents=True, exist_ok=True)
-        with open(markdown_file, "w") as file:
+        with open(markdown_file, "w", encoding="utf-8") as file:
             file.write(md_string)
 
     if html_file:
diff --git a/tests/changelog/integration/test_diffstix_output_generation.py b/tests/changelog/integration/test_diffstix_output_generation.py
index 47ca399..9bb191b 100644
--- a/tests/changelog/integration/test_diffstix_output_generation.py
+++ b/tests/changelog/integration/test_diffstix_output_generation.py
@@ -155,7 +155,7 @@ def test_end_to_end_output_generation(self, minimal_stix_bundles, tmp_path, setu
         assert Path(layer_files[0]).exists()
 
         # Verify markdown file content
-        markdown_content = markdown_file.read_text()
+        markdown_content = markdown_file.read_text(encoding="utf-8")
         assert markdown_content == markdown_result
         assert "## Key" in markdown_content
 
diff --git a/tests/changelog/test_utils.py b/tests/changelog/test_utils.py
index cc0ef42..e97878a 100644
--- a/tests/changelog/test_utils.py
+++ b/tests/changelog/test_utils.py
@@ -230,7 +230,7 @@ def validate_markdown_file_content(file_path: Union[str, Path]) -> str:
     path_obj = Path(file_path)
     assert path_obj.exists(), f"Markdown file should exist at {file_path}"
 
-    content = path_obj.read_text()
+    content = path_obj.read_text(encoding="utf-8")
     assert_basic_markdown_structure(content)
     return content
 
@@ -405,7 +405,7 @@ def validate_comprehensive_output_generation(
 
     # Validate markdown file content matches return value
     if "markdown" in file_paths:
-        file_content = Path(file_paths["markdown"]).read_text()
+        file_content = Path(file_paths["markdown"]).read_text(encoding="utf-8")
         assert file_content == markdown_result, "Markdown file content should match return value"