diff --git a/kenjutsu/format.py b/kenjutsu/format.py
index df231aa..e238354 100644
--- a/kenjutsu/format.py
+++ b/kenjutsu/format.py
@@ -282,4 +282,13 @@ def reformat_slices(slices, lengths=None):
 
         new_slices = tuple(new_slices)
 
+    n_seqs = sum(map(
+        lambda i: isinstance(i, collections.Sequence), new_slices
+    ))
+    if n_seqs > 1:
+        raise ValueError(
+            "Only one integral sequence supported."
+            " Instead got `%s`." % str(n_seqs)
+        )
+
     return(new_slices)
diff --git a/tests/test_format.py b/tests/test_format.py
index ca2aaa0..6f18903 100644
--- a/tests/test_format.py
+++ b/tests/test_format.py
@@ -298,6 +298,16 @@ def test_reformat_slices(self):
             "Only one Ellipsis is permitted. Found multiple."
         )
 
+        with self.assertRaises(ValueError) as e:
+            format.reformat_slices(
+                ([0, 1], [0, 1]),
+            )
+
+        self.assertEqual(
+            str(e.exception),
+            "Only one integral sequence supported. Instead got `2`."
+        )
+
         rf_slice = format.reformat_slices(slice(None))
         self.assertEqual(
             rf_slice,