diff --git a/src/if_py_both.h b/src/if_py_both.h
index 01cbe41..4d81a4b 100644
--- a/src/if_py_both.h
+++ b/src/if_py_both.h
@@ -2326,7 +2326,7 @@
     {
 	Py_ssize_t start, stop, step, slicelen;
 
-	if (PySlice_GetIndicesEx(idx, ListLength(self),
+	if (PySlice_GetIndicesEx((PySliceObject *)idx, ListLength(self),
 				 &start, &stop, &step, &slicelen) < 0)
 	    return NULL;
 	return ListSlice(self, start, step, slicelen);
@@ -2616,7 +2616,7 @@
     {
 	Py_ssize_t start, stop, step, slicelen;
 
-	if (PySlice_GetIndicesEx(idx, ListLength(self),
+	if (PySlice_GetIndicesEx((PySliceObject *)idx, ListLength(self),
 				 &start, &stop, &step, &slicelen) < 0)
 	    return -1;
 	return ListAssSlice(self, start, step, slicelen,