diff --git a/sdutil/sdutil.c b/sdutil/sdutil.c
index 434926d..7567a0e 100644
--- a/sdutil/sdutil.c
+++ b/sdutil/sdutil.c
@@ -29,10 +29,12 @@ struct dos_mbr {
 
 static void start_part_dos (void) {
   char dev_name[64];
+  memset (dev_name, 0, sizeof (dev_name));
   struct dos_mbr mbr;
   memset (&mbr, 0, sizeof (mbr));
-  bool ok = false, write = false;
   char confirm_buf[4];
+  memset (confirm_buf, 0, sizeof (confirm_buf));
+  bool ok = false, write = false;
 
   in_stream_read_line ("Device name: ", dev_name, sizeof (dev_name));