diff --git a/Lib/test/test_curses.py b/Lib/test/test_curses.py
index 6bbb3fc97c4..87c536f0e07 100644
--- a/Lib/test/test_curses.py
+++ b/Lib/test/test_curses.py
@@ -190,6 +190,8 @@ class TestCurses(unittest.TestCase):
 
         self.assertRaises(ValueError, stdscr.getstr, -400)
         self.assertRaises(ValueError, stdscr.getstr, 2, 3, -400)
+        self.assertRaises(ValueError, stdscr.instr, -2)
+        self.assertRaises(ValueError, stdscr.instr, 2, 3, -2)
 
 
     def test_module_funcs(self):
diff --git a/Misc/NEWS b/Misc/NEWS
index d91678005bc..1de23b575fb 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -37,8 +37,8 @@ Library
 - Issue #26750: unittest.mock.create_autospec() now works properly for
   subclasses of property() and other data descriptors.
 
-- In the curses module, raise an error if window.getstr() is passed a negative
-  value.
+- In the curses module, raise an error if window.getstr() or window.instr() is
+  passed a negative value.
 
 - Issue #27760: Fix possible integer overflow in binascii.b2a_qp.
 
diff --git a/Modules/_cursesmodule.c b/Modules/_cursesmodule.c
index 06aa46c3130..960752cce37 100644
--- a/Modules/_cursesmodule.c
+++ b/Modules/_cursesmodule.c
@@ -1393,6 +1393,10 @@ PyCursesWindow_InStr(PyCursesWindowObject *self, PyObject *args)
     case 1:
         if (!PyArg_ParseTuple(args,"i;n", &n))
             return NULL;
+        if (n < 0) {
+            PyErr_SetString(PyExc_ValueError, "'n' must be nonnegative");
+            return NULL;
+        }
         rtn2 = winnstr(self->win, rtn, Py_MIN(n, 1023));
         break;
     case 2:
@@ -1403,6 +1407,10 @@ PyCursesWindow_InStr(PyCursesWindowObject *self, PyObject *args)
     case 3:
         if (!PyArg_ParseTuple(args, "iii;y,x,n", &y, &x, &n))
             return NULL;
+        if (n < 0) {
+            PyErr_SetString(PyExc_ValueError, "'n' must be nonnegative");
+            return NULL;
+        }
         rtn2 = mvwinnstr(self->win, y, x, rtn, Py_MIN(n,1023));
         break;
     default: