diff --git a/coverage_comment/github_client.py b/coverage_comment/github_client.py
index 19165b64..526393e2 100644
--- a/coverage_comment/github_client.py
+++ b/coverage_comment/github_client.py
@@ -47,7 +47,6 @@ def __getattr__(self, attr):
 
 
 class GitHub:
-
     """
     GitHub client.
     """
@@ -61,6 +60,8 @@ def __getattr__(self, attr):
     def _http(self, method, path, *, bytes=False, **kw):
         _method = method.lower()
         requests_kwargs = {}
+        headers = kw.pop("headers", {})
+        header_kwargs = {"headers": headers} if headers else {}
         if _method == "get" and kw:
             requests_kwargs = {"params": kw}
 
@@ -71,6 +72,7 @@ def _http(self, method, path, *, bytes=False, **kw):
             _method.upper(),
             path,
             timeout=TIMEOUT,
+            **header_kwargs,
             **requests_kwargs,
         )
         if bytes:
diff --git a/coverage_comment/storage.py b/coverage_comment/storage.py
index 72357645..eb8e49a0 100644
--- a/coverage_comment/storage.py
+++ b/coverage_comment/storage.py
@@ -1,6 +1,5 @@
 from __future__ import annotations
 
-import base64
 import contextlib
 import pathlib
 
@@ -120,11 +119,16 @@ def get_datafile_contents(
 ) -> str | None:
     contents_path = github.repos(repository).contents(str(files.DATA_PATH))
     try:
-        response = contents_path.get(ref=branch)
+        response = contents_path.get(
+            ref=branch,
+            # If we don't pass this header, the format of the answer will depend on
+            # the size of the file. With the header, we're sure to get the raw content.
+            headers={"Accept": "application/vnd.github.raw+json"},
+        )
     except github_client.NotFound:
         return None
 
-    return base64.b64decode(response.content).decode()
+    return response
 
 
 def get_raw_file_url(
diff --git a/tests/unit/test_github_client.py b/tests/unit/test_github_client.py
index 8aa147eb..94f1ce9b 100644
--- a/tests/unit/test_github_client.py
+++ b/tests/unit/test_github_client.py
@@ -13,6 +13,15 @@ def test_github_client__get(session, gh):
     assert gh.repos("a/b").issues().get(a=1) == {"foo": "bar"}
 
 
+def test_github_client__get_headers(session, gh):
+    session.register("GET", "/repos/a/b/issues", timeout=60, params={"a": 1})(
+        json={"foo": "bar"},
+        headers={"X-foo": "yay"},
+    )
+
+    assert gh.repos("a/b").issues().get(a=1, headers={"X-foo": "yay"}) == {"foo": "bar"}
+
+
 def test_github_client__post_non_json(session, gh):
     session.register("POST", "/repos/a/b/issues", timeout=60, json={"a": 1})()