diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py
--- a/Lib/test/test_deque.py
+++ b/Lib/test/test_deque.py
@@ -304,6 +304,11 @@
             s.insert(i, 'Z')
             self.assertEqual(list(d), s)
 
+    def test_insert_bug_26194(self):
+        d = deque(range(10), maxlen=10)
+        with self.assertRaises(IndexError):
+            d.insert(0, None)
+
     def test_imul(self):
         for n in (-10, -1, 0, 1, 2, 10, 1000):
             d = deque()
diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c
--- a/Modules/_collectionsmodule.c
+++ b/Modules/_collectionsmodule.c
@@ -1089,6 +1089,11 @@
 
     if (!PyArg_ParseTuple(args, "nO:insert", &index, &value))
         return NULL;
+    if (deque->maxlen == Py_SIZE(deque)) {
+        PyErr_SetString(PyExc_IndexError,
+            "cannot insert new value, deque is already at its maximum length");
+        return NULL;
+    }
     if (index >= n)
         return deque_append(deque, value);
     if (index <= -n || index == 0)