diff --git a/src/c/_cffi_backend.c b/src/c/_cffi_backend.c
index 6087e635..6a2d4957 100644
--- a/src/c/_cffi_backend.c
+++ b/src/c/_cffi_backend.c
@@ -2609,6 +2609,11 @@ cdata_ass_slice(CDataObject *cd, PySliceObject *slice, PyObject *v)
     cdata = cd->c_data + itemsize * bounds[0];
     length = bounds[1];
 
+    if (v == NULL) {
+        PyErr_SetString(PyExc_TypeError,
+                        "'del x[n]' not supported for cdata objects");
+        return -1;
+    }
     if (CData_Check(v)) {
         CTypeDescrObject *ctv = ((CDataObject *)v)->c_type;
         if ((ctv->ct_flags & CT_ARRAY) && (ctv->ct_itemdescr == ct) &&
diff --git a/src/c/minibuffer.h b/src/c/minibuffer.h
index a6d40e4f..89e400fa 100644
--- a/src/c/minibuffer.h
+++ b/src/c/minibuffer.h
@@ -243,6 +243,11 @@ static PyObject *mb_subscript(MiniBufferObj *self, PyObject *item)
 static int
 mb_ass_subscript(MiniBufferObj* self, PyObject* item, PyObject* value)
 {
+    if (value == NULL) {
+        PyErr_SetString(PyExc_TypeError,
+                        "'del x[n]' not supported for buffer objects");
+        return -1;
+    }
     if (PyIndex_Check(item)) {
         Py_ssize_t i = PyNumber_AsSsize_t(item, PyExc_IndexError);
         if (i == -1 && PyErr_Occurred())