diff --git a/debian/patches/core_in_fs.patch b/debian/patches/core_in_fs.patch
index 691866511..ea6db6569 100644
--- a/debian/patches/core_in_fs.patch
+++ b/debian/patches/core_in_fs.patch
@@ -20,12 +20,13 @@ Index: b/util/setup.c
      goto finish;
    }
  
-@@ -619,6 +623,9 @@
+@@ -619,6 +623,10 @@
    /* The core image must be put on a filesystem unfortunately.  */
    grub_util_info ("will leave the core image on the filesystem");
  
-+  fp = fopen (DEFAULT_DIRECTORY "/" CORE_IMG_IN_FS, "w");
-+  fclose (fp);
++  fp = grub_util_fd_open (DEFAULT_DIRECTORY "/" CORE_IMG_IN_FS,
++			  GRUB_UTIL_FD_O_WRONLY);
++  grub_util_fd_close (fp);
 +
    grub_util_biosdisk_flush (root_dev->disk);
  
diff --git a/util/setup.c b/util/setup.c
index 79a88f770..60d46e847 100644
--- a/util/setup.c
+++ b/util/setup.c
@@ -623,8 +623,9 @@ unable_to_embed:
   /* The core image must be put on a filesystem unfortunately.  */
   grub_util_info ("will leave the core image on the filesystem");
 
-  fp = fopen (DEFAULT_DIRECTORY "/" CORE_IMG_IN_FS, "w");
-  fclose (fp);
+  fp = grub_util_fd_open (DEFAULT_DIRECTORY "/" CORE_IMG_IN_FS,
+			  GRUB_UTIL_FD_O_WRONLY);
+  grub_util_fd_close (fp);
 
   grub_util_biosdisk_flush (root_dev->disk);