diff --git a/internetarchive/cli/ia_upload.py b/internetarchive/cli/ia_upload.py
index 26a47f7f..9eab9686 100644
--- a/internetarchive/cli/ia_upload.py
+++ b/internetarchive/cli/ia_upload.py
@@ -77,7 +77,8 @@
 
 from internetarchive.cli.argparser import get_args_dict, convert_str_list_to_unicode
 from internetarchive.session import ArchiveSession
-from internetarchive.utils import validate_s3_identifier, get_s3_xml_text, InvalidIdentifierException
+from internetarchive.utils import (InvalidIdentifierException, get_s3_xml_text,
+                                   is_valid_metadata_key, validate_s3_identifier)
 
 # Only import backports.csv for Python2 (in support of FreeBSD port).
 PY2 = sys.version_info[0] == 2
@@ -263,6 +264,11 @@ def main(argv, session):
             spreadsheet = csv.DictReader(csvfp)
             prev_identifier = None
             for row in spreadsheet:
+                for metadata_key in row:
+                    if not is_valid_metadata_key(metadata_key):
+                        print('error: "%s" is not a valid metadata key.' % metadata_key,
+                              file=sys.stderr)
+                        sys.exit(1)
                 upload_kwargs_copy = deepcopy(upload_kwargs)
                 if row.get('REMOTE_NAME'):
                     local_file = {row['REMOTE_NAME']: row['file']}
@@ -271,7 +277,8 @@ def main(argv, session):
                     local_file = row['file']
                 identifier = row.get('item', row.get('identifier'))
                 if not identifier:
-                    print('error: no identifier column on spreadsheet!')
+                    print('error: no identifier column on spreadsheet.',
+                          file=sys.stderr)
                     sys.exit(1)
                 del row['file']
                 if 'identifier' in row:
diff --git a/internetarchive/utils.py b/internetarchive/utils.py
index dc973f02..d0d61deb 100644
--- a/internetarchive/utils.py
+++ b/internetarchive/utils.py
@@ -358,3 +358,14 @@ def delete_items_from_dict(d, to_delete):
         for i in d:
             delete_items_from_dict(i, to_delete)
     return remove_none(d)
+
+
+def is_valid_metadata_key(name):
+    # According to the documentation a metadata key
+    # has to be a valid XML tag name.
+    #
+    # The actual allowed tag names (at least as tested with the metadata API),
+    # are way more restrictive and only allow ".-A-Za-z_", possibly followed
+    # by an index in square brackets e. g. [0].
+    # On the other hand the Archive allows tags starting with the string "xml".
+    return bool(re.fullmatch('[A-Za-z][.\-0-9A-Za-z_]+(?:\[[0-9]+\])?', name))
diff --git a/pex-requirements.txt b/pex-requirements.txt
index 9a6e9089..0679e4c3 100644
--- a/pex-requirements.txt
+++ b/pex-requirements.txt
@@ -1,8 +1,8 @@
-requests>=2.9.1,<3.0.0
-jsonpatch>=0.4
+backports.csv
 docopt>=0.6.0,<0.7.0
-tqdm>=4.0.0
-six>=1.13.0,<2.0.0
+jsonpatch>=0.4
+requests>=2.9.1,<3.0.0
 schema>=0.4.0
-backports.csv
 setuptools
+six>=1.13.0,<2.0.0
+tqdm>=4.0.0
diff --git a/setup.py b/setup.py
index 92a4835c..ddf7f99d 100644
--- a/setup.py
+++ b/setup.py
@@ -36,13 +36,13 @@
         ],
     },
     install_requires=[
-        'requests>=2.9.1,<3.0.0',
-        'jsonpatch>=0.4',
+        'backports.csv < 1.07;python_version<"3.4"',
         'docopt>=0.6.0,<0.7.0',
-        'tqdm>=4.0.0',
-        'six>=1.13.0,<2.0.0',
+        'jsonpatch>=0.4',
+        'requests>=2.9.1,<3.0.0',
         'schema>=0.4.0',
-        'backports.csv < 1.07;python_version<"3.4"',
+        'six>=1.13.0,<2.0.0',
+        'tqdm>=4.0.0',
     ],
     classifiers=[
         'Development Status :: 5 - Production/Stable',