diff --git a/pyss3/__init__.py b/pyss3/__init__.py
index 6abca2b..1462874 100644
--- a/pyss3/__init__.py
+++ b/pyss3/__init__.py
@@ -1959,7 +1959,7 @@ def classify_label(self, doc, def_cat=STR_MOST_PROBABLE, labels=True, prep=True)
         """
         r = self.classify(doc, sort=True, prep=prep)
 
-        if not r[0][1]:
+        if not r or not r[0][1]:
             if not def_cat or def_cat == STR_UNKNOWN:
                 cat = STR_UNKNOWN_CATEGORY
             elif def_cat == STR_MOST_PROBABLE:
@@ -1999,7 +1999,7 @@ def classify_multilabel(self, doc, def_cat=STR_MOST_PROBABLE, labels=True, prep=
         """
         r = self.classify(doc, sort=True, prep=prep)
 
-        if not r[0][1]:
+        if not r or not r[0][1]:
             if not def_cat or def_cat == STR_UNKNOWN:
                 cat = STR_UNKNOWN_CATEGORY
             elif def_cat == STR_MOST_PROBABLE:
diff --git a/tests/test_pyss3.py b/tests/test_pyss3.py
index e5be0cd..e0eb5ca 100644
--- a/tests/test_pyss3.py
+++ b/tests/test_pyss3.py
@@ -139,6 +139,10 @@ def perform_tests_with(clf, cv_test, stopwords=True):
     assert clf.classify_label(x_test[0]) == y_test[0]
     assert clf.classify_label(x_test[0], labels=False) == clf.get_category_index(y_test[0])
 
+    assert clf.classify_label('') == most_prob_cat
+    assert clf.classify_label('', def_cat=STR_UNKNOWN) == STR_UNKNOWN_CATEGORY
+    assert clf.classify_label('', def_cat=def_cat) == def_cat
+
     assert clf.classify_label(doc_unknown) == most_prob_cat
     assert clf.classify_label(doc_unknown, def_cat=STR_UNKNOWN) == STR_UNKNOWN_CATEGORY
     assert clf.classify_label(doc_unknown, def_cat=def_cat) == def_cat
@@ -156,6 +160,10 @@ def perform_tests_with(clf, cv_test, stopwords=True):
     assert len(multilabel_labels) == len(r)
     assert r[0] in multilabel_idxs and r[1] in multilabel_idxs
 
+    assert clf.classify_multilabel('') == [most_prob_cat]
+    assert clf.classify_multilabel('', def_cat=STR_UNKNOWN) == [pyss3.STR_UNKNOWN_CATEGORY]
+    assert clf.classify_multilabel('', def_cat=def_cat) == [def_cat]
+
     assert clf.classify_multilabel(doc_unknown) == [most_prob_cat]
     assert clf.classify_multilabel(doc_unknown, def_cat=STR_UNKNOWN) == [pyss3.STR_UNKNOWN_CATEGORY]
     assert clf.classify_multilabel(doc_unknown, def_cat=def_cat) == [def_cat]