diff --git a/Modules/dbmmodule.c b/Modules/dbmmodule.c
index fb6c7b6..c91ea47 100644
--- a/Modules/dbmmodule.c
+++ b/Modules/dbmmodule.c
@@ -166,7 +166,8 @@
 {
 	datum key, val;
 
-	if (PyString_AsStringAndSize(v, &key.dptr, &key.dsize)) {
+	if (PyString_AsStringAndSize(v, (char **)&key.dptr,
+	                             (Py_ssize_t *)&key.dsize)) {
 		return -1;
 	}