diff --git a/Modules/sha1module.c b/Modules/sha1module.c
index b21b21d..7d97e4f 100644
--- a/Modules/sha1module.c
+++ b/Modules/sha1module.c
@@ -488,6 +488,7 @@
     static char *kwlist[] = {"string", NULL};
     SHA1object *new;
     Py_buffer buf;
+    buf.buf = NULL;
 
     if (!PyArg_ParseTupleAndKeywords(args, kwdict, "|s*:new", kwlist,
                                      &buf)) {