diff --git a/miniflux.py b/miniflux.py
index 05c2e93..9c1c2f6 100644
--- a/miniflux.py
+++ b/miniflux.py
@@ -49,7 +49,8 @@ def get_error_reason(self) -> str:
             str: The error message from the response body, or a default message if not available.
         """
         default_reason = f"status_code={self.status_code}"
-        if self._response.headers.get("Content-Type") == "application/json":
+        content_type = self._response.headers.get("Content-Type", "")
+        if content_type.startswith("application/json"):
             result = self._response.json()
             if isinstance(result, dict):
                 return result.get("error_message", default_reason)
diff --git a/tests/test_client.py b/tests/test_client.py
index d4a099d..39b11e2 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -89,6 +89,14 @@ def test_get_error_with_bad_response(self):
         self.assertEqual(error.status_code, 404)
         self.assertEqual(error.get_error_reason(), "status_code=404")
 
+    def test_get_error_reason_with_charset_in_content_type(self):
+        response = mock.Mock()
+        response.status_code = 400
+        response.headers = {"Content-Type": "application/json; charset=utf-8"}
+        response.json.return_value = {"error_message": "invalid input"}
+        error = BadRequest(response)
+        self.assertEqual(error.get_error_reason(), "invalid input")
+
     def test_get_error_reason_without_json_content_type(self):
         response = mock.Mock()
         response.status_code = 500