diff --git a/asdf/_asdf.py b/asdf/_asdf.py
index 41dac5bed..d757ff357 100644
--- a/asdf/_asdf.py
+++ b/asdf/_asdf.py
@@ -75,7 +75,7 @@ def __init__(
         ignore_version_mismatch=NotSet,
         ignore_unrecognized_tag=False,
         ignore_implicit_conversion=NotSet,
-        memmap=True,
+        memmap=False,
         lazy_load=True,
         custom_schema=None,
     ):
@@ -118,7 +118,7 @@ def __init__(
 
         memmap : bool, optional
             When `True`, when reading files, attempt to memmap underlying data
-            arrays when possible. Defaults to ``True``.
+            arrays when possible. Defaults to ``False``.
 
         lazy_load : bool, optional
             When `True` and the underlying file handle is seekable, data
@@ -1610,7 +1610,7 @@ def open_asdf(
     ignore_version_mismatch=NotSet,
     ignore_unrecognized_tag=False,
     _force_raw_types=False,
-    memmap=True,
+    memmap=False,
     lazy_tree=NotSet,
     lazy_load=True,
     custom_schema=None,
@@ -1654,7 +1654,7 @@ def open_asdf(
 
     memmap : bool, optional
         When `True`, when reading files, attempt to memmap underlying data
-        arrays when possible. Defaults to ``True``.
+        arrays when possible. Defaults to ``False``.
 
     lazy_load : bool, optional
         When `True` and the underlying file handle is seekable, data