diff --git a/genome_kit/diseq.py b/genome_kit/diseq.py
index 28366658..a8d8fbf3 100644
--- a/genome_kit/diseq.py
+++ b/genome_kit/diseq.py
@@ -1046,6 +1046,10 @@ def dna(self, allow_outside_coord: bool = True) -> str:
             If the segment extends past the coord intervals and
             ``allow_outside_coord`` is False.
         """
+        if type(allow_outside_coord) is not bool:
+            raise TypeError(
+                f"allow_outside_coord must be a bool, got {type(allow_outside_coord).__name__}"
+            )
         if self._start == self._end:
             return ""
 
diff --git a/tests/test_diseq.py b/tests/test_diseq.py
index 9c1e76d9..f7a9e764 100644
--- a/tests/test_diseq.py
+++ b/tests/test_diseq.py
@@ -2663,6 +2663,13 @@ def test_off_coord_strand_minus_coord_multi_interval(self):
         )
         self.assertEqual(dis.dna(), expected)
 
+    def test_passing_non_bool_raises(self):
+        ivs = _make_intervals([("chr1", "+", 100, 200)])
+        dis = DisjointIntervalSequence(ivs, on_coordinate_strand=False, start=0, end=50)
+        dis2 = dis.cut(10, 20)
+        with self.assertRaises(TypeError):
+            dis.dna(dis2)
+
 
 if __name__ == "__main__":
     unittest.main()