diff --git a/grub-core/commands/verify.c b/grub-core/commands/verify.c
index d5995766b..656939189 100644
--- a/grub-core/commands/verify.c
+++ b/grub-core/commands/verify.c
@@ -308,7 +308,7 @@ grub_load_public_key (grub_file_t f)
       if (!sk)
 	goto fail;
 
-      grub_memset (fingerprint_context, 0, sizeof (fingerprint_context));
+      grub_memset (fingerprint_context, 0, GRUB_MD_SHA1->contextsize);
       GRUB_MD_SHA1->init (fingerprint_context);
       GRUB_MD_SHA1->write (fingerprint_context, "\x99", 1);
       len_be = grub_cpu_to_be16 (len);