diff --git a/CHANGES.rst b/CHANGES.rst
index f9c338f4..f4d66992 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,6 +1,12 @@
 1.6 (unreleased)
 ================
 
+Bug Fixes
+---------
+
+- cachedataset() and friends again produce reasonable file extensions.
+  [#553]
+
 Enhancements and Fixes
 ----------------------
 
diff --git a/pyvo/dal/mimetype.py b/pyvo/dal/mimetype.py
index a78fb44e..863b861f 100644
--- a/pyvo/dal/mimetype.py
+++ b/pyvo/dal/mimetype.py
@@ -25,8 +25,11 @@ def mime2extension(mimetype, default=None):
     implementations of ``suggest_extension()`` in ``Record`` subclasses.
 
       >>> mime2extension('application/fits')
+      'fits'
       >>> mime2extension('image/jpeg')
+      'jpg'
       >>> mime2extension('application/x-zed', 'dat')
+      'dat'
 
     Parameters
     ----------
@@ -46,11 +49,14 @@ def mime2extension(mimetype, default=None):
     if not mimetype:
         return default
 
-    if isinstance(mimetype, str):
-        mimetype = mimetype.encode('utf-8')
+    if isinstance(mimetype, bytes):
+        mimetype = mimetype.decode('utf-8')
 
     ext = mimetypes.guess_extension(mimetype, strict=False)
-    return ext
+    if ext is None:
+        return default
+
+    return ext.lstrip(".")
 
 
 def mime_object_maker(url, mimetype, *, session=None):
diff --git a/pyvo/dal/sia.py b/pyvo/dal/sia.py
index dc861f36..e42f34db 100644
--- a/pyvo/dal/sia.py
+++ b/pyvo/dal/sia.py
@@ -915,7 +915,7 @@ def suggest_dataset_basename(self):
             out = re.sub(r'\s+', '_', out.strip())
         return out
 
-    def suggest_extension(self, *, default=None):
+    def suggest_extension(self, *, default='dat'):
         """
         returns a recommended filename extension for the dataset described
         by this record.  Typically, this would look at the column describing