diff --git a/CHANGES.rst b/CHANGES.rst
index c6158ea041..50864483af 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -29,6 +29,11 @@ esa.emds.einsteinprobe
 API changes
 -----------
 
+heasarc
+^^^^^^^^^^
+
+- Ensure 'astroquery' is in the request headers. [#3439]
+
 esa.utils
 ^^^^^^^^^^
 
diff --git a/astroquery/heasarc/core.py b/astroquery/heasarc/core.py
index 2406e274a9..6605ad5f34 100644
--- a/astroquery/heasarc/core.py
+++ b/astroquery/heasarc/core.py
@@ -38,7 +38,6 @@ def __init__(self):
         self._tap = None
         self._datalink = None
         self._meta_info = None
-        self._session = None
 
     @property
     def tap(self):