diff --git a/ChangeLog b/ChangeLog
index 31020644e..9162f2bdd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2010-07-05  Colin Watson  <cjwatson@ubuntu.com>
+
+	* util/i386/pc/grub-setup.c (setup): Rename prefix to
+	install_prefix, in line with install_dos_part and install_bsd_part.
+	Add new prefix variable, which is copied to install_prefix after
+	comparing core.img in memory with the one read from disk in the
+	no-embedding case, and use that rather than overwriting
+	install_prefix immediately when installing to a partition.
+	Fixes Debian bug #586621; based on patches by Matt Kraai and M. Vefa
+	Bicakci.
+
 2010-07-04  Grégoire Sutre  <gregoire.sutre@gmail.com>
 
 	* configure.ac: Avoid == in test command, it's not portable.
diff --git a/util/i386/pc/grub-setup.c b/util/i386/pc/grub-setup.c
index 3fe7d5622..8b2f52bb4 100644
--- a/util/i386/pc/grub-setup.c
+++ b/util/i386/pc/grub-setup.c
@@ -102,7 +102,8 @@ setup (const char *dir,
   struct grub_boot_blocklist *first_block, *block;
   grub_int32_t *install_dos_part, *install_bsd_part;
   grub_int32_t dos_part, bsd_part;
-  char *prefix;
+  char *install_prefix;
+  char *prefix = NULL;
   char *tmp_img;
   int i;
   grub_disk_addr_t first_sector;
@@ -234,8 +235,8 @@ setup (const char *dir,
 				       + GRUB_KERNEL_MACHINE_INSTALL_DOS_PART);
   install_bsd_part = (grub_int32_t *) (core_img + GRUB_DISK_SECTOR_SIZE
 				       + GRUB_KERNEL_MACHINE_INSTALL_BSD_PART);
-  prefix = (char *) (core_img + GRUB_DISK_SECTOR_SIZE +
-		     GRUB_KERNEL_MACHINE_PREFIX);
+  install_prefix = (char *) (core_img + GRUB_DISK_SECTOR_SIZE +
+			     GRUB_KERNEL_MACHINE_PREFIX);
 
   /* Open the root device and the destination device.  */
   root_dev = grub_device_open (root);
@@ -312,15 +313,13 @@ setup (const char *dir,
  	      bsd_part = -1;
  	    }
 
-	  if (prefix[0] != '(')
+	  if (install_prefix[0] != '(')
 	    {
-	      char *root_part_name, *new_prefix;
+	      char *root_part_name;
 
 	      root_part_name =
 		grub_partition_get_name (root_dev->disk->partition);
-	      new_prefix = xasprintf ("(,%s)%s", root_part_name, prefix);
-	      strcpy (prefix, new_prefix);
-	      free (new_prefix);
+	      prefix = xasprintf ("(,%s)%s", root_part_name, install_prefix);
 	      free (root_part_name);
 	    }
 	}
@@ -411,6 +410,8 @@ setup (const char *dir,
 
   *install_dos_part = grub_cpu_to_le32 (dos_part);
   *install_bsd_part = grub_cpu_to_le32 (bsd_part);
+  if (prefix)
+    strcpy (install_prefix, prefix);
 
   /* The first blocklist contains the whole sectors.  */
   first_block->start = grub_cpu_to_le64 (embed_region.start + 1);
@@ -571,6 +572,8 @@ unable_to_embed:
 
   *install_dos_part = grub_cpu_to_le32 (dos_part);
   *install_bsd_part = grub_cpu_to_le32 (bsd_part);
+  if (prefix)
+    strcpy (install_prefix, prefix);
 
   /* Write the first two sectors of the core image onto the disk.  */
   grub_util_info ("opening the core image `%s'", core_path);
@@ -590,6 +593,7 @@ unable_to_embed:
   /* Sync is a Good Thing.  */
   sync ();
 
+  free (prefix);
   free (core_path);
   free (core_img);
   free (boot_img);