diff --git a/asdf/_asdf.py b/asdf/_asdf.py
index f7056ab51..ad9de9223 100644
--- a/asdf/_asdf.py
+++ b/asdf/_asdf.py
@@ -1623,7 +1623,7 @@ def open_asdf(
     ignore_unrecognized_tag=False,
     _force_raw_types=False,
     copy_arrays=NotSet,
-    memmap=True,
+    memmap=NotSet,
     lazy_tree=NotSet,
     lazy_load=True,
     custom_schema=None,
diff --git a/asdf/_tests/test_array_blocks.py b/asdf/_tests/test_array_blocks.py
index 2efc4d85b..32cb03491 100644
--- a/asdf/_tests/test_array_blocks.py
+++ b/asdf/_tests/test_array_blocks.py
@@ -816,12 +816,13 @@ def filename_with_array(tmp_path_factory):
         ({"memmap": False}, False),
         ({"copy_arrays": True}, False),
         ({"copy_arrays": False}, True),
-        ({"memmap": True, "copy_arrays": True}, True),
-        ({"memmap": True, "copy_arrays": False}, True),
-        ({"memmap": False, "copy_arrays": True}, False),
-        ({"memmap": False, "copy_arrays": False}, False),
+        ({"copy_arrays": True, "memmap": True}, True),
+        ({"copy_arrays": False, "memmap": True}, True),
+        ({"copy_arrays": True, "memmap": False}, False),
+        ({"copy_arrays": False, "memmap": False}, False),
     ],
 )
+@pytest.mark.filterwarnings("ignore:copy_arrays is deprecated")
 def test_open_no_memmap(filename_with_array, open_kwargs, should_memmap):
     """
     Test that asdf.open does not (or does) return memmaps for arrays
diff --git a/asdf/_tests/test_deprecated.py b/asdf/_tests/test_deprecated.py
index 711c2c9df..55bb02d13 100644
--- a/asdf/_tests/test_deprecated.py
+++ b/asdf/_tests/test_deprecated.py
@@ -6,7 +6,7 @@
 
 import asdf
 import asdf.testing.helpers
-from asdf.exceptions import AsdfDeprecationWarning, ValidationError
+from asdf.exceptions import AsdfDeprecationWarning, AsdfWarning, ValidationError
 
 
 def test_asdf_stream_deprecation():
@@ -155,6 +155,6 @@ def test_copy_arrays_deprecation(copy_arrays, memmap, tmp_path):
     af = asdf.AsdfFile()
     af["a"] = 1
     af.write_to(fn)
-    with pytest.warns(AsdfDeprecationWarning, match="copy_arrays is deprecated; use memmap instead"):
+    with pytest.warns(AsdfWarning, match="copy_arrays is deprecated; use memmap instead"):
         with asdf.open(fn, copy_arrays=copy_arrays, memmap=memmap) as af:
             pass