diff --git a/kitty/line-buf.c b/kitty/line-buf.c
index 854d00ccb..459a60e6b 100644
--- a/kitty/line-buf.c
+++ b/kitty/line-buf.c
@@ -292,6 +292,7 @@ copy_line_to(LineBuf *self, PyObject *args) {
     unsigned int y;
     Line src, *dest;
     if (!PyArg_ParseTuple(args, "IO!", &y, &Line_Type, &dest)) return NULL;
+    if (y >= self->ynum) { PyErr_SetString(PyExc_ValueError, "Out of bounds"); return NULL; }
     src.xnum = self->xnum; dest->xnum = self->xnum;
     dest->ynum = y;
     dest->attrs = self->line_attrs[y];
diff --git a/kitty_tests/datatypes.py b/kitty_tests/datatypes.py
index cc462d647..d82495076 100644
--- a/kitty_tests/datatypes.py
+++ b/kitty_tests/datatypes.py
@@ -279,6 +279,8 @@ class TestDataTypes(BaseTest):
         l2 = lb.create_line_copy(2)
         lb.copy_line_to(1, l2)
         self.ae(l2, lb2.line(2))
+        with self.assertRaises(ValueError):
+            lb.copy_line_to(lb.ynum, l2)
         lb.clear_line(0)
         self.ae(lb.line(0), LineBuf(1, lb.xnum).create_line_copy(0))
         lb = filled_line_buf(5, 5, filled_cursor())