diff --git a/annif/corpus/document.py b/annif/corpus/document.py
index 157d033de..f29fc2ddb 100644
--- a/annif/corpus/document.py
+++ b/annif/corpus/document.py
@@ -5,10 +5,12 @@
 import re
 import gzip
 import annif.util
-from .types import Document, DocumentCorpus
+from .types import DocumentCorpus
 from .convert import DocumentToSubjectCorpusMixin
 from .subject import SubjectSet
 
+logger = annif.logger
+
 
 class DocumentDirectory(DocumentCorpus, DocumentToSubjectCorpusMixin):
     """A directory of files as a full text document corpus"""
@@ -61,15 +63,21 @@ def opener(path):
                 return gzip.open(path, mode='rt')
         else:
             opener = open
-
         with opener(self.path) as tsvfile:
             for line in tsvfile:
-                text, uris = line.split('\t', maxsplit=1)
-                subjects = [annif.util.cleanup_uri(uri)
-                            for uri in uris.split()]
-                yield self._create_document(text=text,
-                                            uris=subjects,
-                                            labels=[])
+                yield from self._parse_tsv_line(line)
+
+    def _parse_tsv_line(self, line):
+        if '\t' in line:
+            text, uris = line.split('\t', maxsplit=1)
+            subjects = [annif.util.cleanup_uri(uri)
+                        for uri in uris.split()]
+            yield self._create_document(text=text,
+                                        uris=subjects,
+                                        labels=[])
+        else:
+            logger.warning('Skipping invalid line (missing tab): "%s"',
+                           line.rstrip())
 
 
 class DocumentList(DocumentCorpus, DocumentToSubjectCorpusMixin):
diff --git a/tests/test_corpus.py b/tests/test_corpus.py
index 9d8e2971e..4f7928aff 100644
--- a/tests/test_corpus.py
+++ b/tests/test_corpus.py
@@ -218,6 +218,23 @@ def test_docfile_plain(tmpdir):
     assert len(list(docs.documents)) == 3
 
 
+def test_docfile_plain_invalid_lines(tmpdir, caplog):
+    logger = annif.logger
+    logger.propagate = True
+    docfile = tmpdir.join('documents_invalid.tsv')
+    docfile.write("""Läntinen\t<http://www.yso.fi/onto/yso/p2557>
+
+        Oulunlinnan\t<http://www.yso.fi/onto/yso/p7346>
+        A line with no tabs
+        Harald Hirmuinen\t<http://www.yso.fi/onto/yso/p6479>""")
+    docs = annif.corpus.DocumentFile(str(docfile))
+    assert len(list(docs.documents)) == 3
+    assert len(caplog.records) == 2
+    expected_msg = 'Skipping invalid line (missing tab):'
+    for record in caplog.records:
+        assert expected_msg in record.message
+
+
 def test_docfile_gzipped(tmpdir):
     docfile = tmpdir.join('documents.tsv.gz')
     with gzip.open(str(docfile), 'wt') as gzf: