diff --git a/WorkbenchConfig.py b/WorkbenchConfig.py
index 3ae59bd7..642b9930 100644
--- a/WorkbenchConfig.py
+++ b/WorkbenchConfig.py
@@ -26,6 +26,12 @@ def __init__(self, args):
     def get_config(self):
         config = self.get_default_config()
         user_mods = self.get_user_config()
+        # Allow extension additions and overrides.
+        if user_mods.get('mimetype_extensions'):
+            for candidate in user_mods.get('mimetype_extensions'):
+                for mimetype, extension in candidate.items():
+                    config['mimetype_extensions'][mimetype] = extension
+            del user_mods['mimetype_extensions']
         # Blend defaults with user mods
         for key, value in user_mods.items():
             config[key] = value
@@ -87,6 +93,17 @@ def get_media_types(self):
             {'extracted_text': ['txt']}
         ]
 
+    # Returns default file extensions for mimetypes
+    def get_default_extensions(self):
+        return {'image/jpeg': '.jpg',
+                'image/jp2': '.jp2',
+                'image/png': '.png',
+                'audio/mpeg': '.mp3',
+                'audio/mp3': '.mp3',
+                'text/plain': '.txt',
+                'application/octet-stream': '.bin'
+                }
+
     # Returns default configs, to be updated by user-supplied config.
     def get_default_config(self):
         return {
@@ -143,6 +160,7 @@ def get_default_config(self):
             'paged_content_sequence_separator': '-',
             'media_bundle_file_fields': self.get_media_fields(),
             'media_fields': self.get_media_fields(),
+            'mimetype_extensions': self.get_default_extensions(),
         }
 
     # Tests validity and existence of path.
diff --git a/workbench_utils.py b/workbench_utils.py
index 24769616..c88793d0 100644
--- a/workbench_utils.py
+++ b/workbench_utils.py
@@ -2003,7 +2003,7 @@ def create_media(config, filename, file_fieldname, node_id, node_csv_row, media_
         media_type = set_media_type(config, filename, file_fieldname, node_csv_row)
         media_bundle_response_code = ping_media_bundle(config, media_type)
         if media_bundle_response_code == 404:
-            message = 'File "' + file_check_row[filename_field] + '" identified in CSV row ' + file_check_row[config['id_field']] + \
+            message = 'File "' + node_csv_row[file_fieldname] + '" identified in CSV row ' + node_csv_row[config['id_field']] + \
                 ' will create a media of type (' + media_type + '), but that media type is not configured in the destination Drupal.'
             logging.error(message)
             return False
@@ -4032,21 +4032,19 @@ def get_csv_from_excel(config):
     csv_writer_file_handle.close()
 
 
-def get_extension_from_mimetype(mimetype):
+def get_extension_from_mimetype(config, mimetype):
     # mimetypes.add_type() is not working, e.g. mimetypes.add_type('image/jpeg', '.jpg')
     # Maybe related to https://bugs.python.org/issue4963? In the meantime, provide our own
     # MIMETYPE to extension mapping for common types, then let mimetypes guess at others.
-    map = {'image/jpeg': '.jpg',
-           'image/jp2': '.jp2',
-           'image/png': '.png',
-           'audio/mpeg': '.mp3',
-           'text/plain': '.txt',
-           'application/octet-stream': '.bin'
-           }
+    map = config['mimetype_extensions']
     if mimetype in map:
         return map[mimetype]
     else:
-        return mimetypes.guess_extension(mimetype)
+        extension = mimetypes.guess_extension(mimetype)
+        if (extension):
+            return mimetypes.guess_extension(mimetype)
+        else:
+            print(f"There is no mapping available for  {mimetype}")
 
 
 def get_deduped_file_path(path):
@@ -4121,7 +4119,7 @@ def check_file_exists(config, filename):
             return True
 
 
-def get_prepocessed_file_path(config, file_fieldname, node_csv_row, node_id = None):
+def get_prepocessed_file_path(config, file_fieldname, node_csv_row, node_id=None):
     """For remote/downloaded files, generates the path to the local temporary
        copy and returns that path. For local files, just returns the value of
        node_csv_row['file'].
@@ -4193,7 +4191,7 @@ def get_prepocessed_file_path(config, file_fieldname, node_csv_row, node_id = No
             except KeyError:
                 mimetype = 'application/octet-stream'
 
-            extension_with_dot = get_extension_from_mimetype(mimetype)
+            extension_with_dot = get_extension_from_mimetype(config, mimetype)
             downloaded_file_path = os.path.join(subdir, filename + extension_with_dot)
 
             # Check to see if a file with this path already exists; if so, insert an