diff --git a/grub-core/fs/hfsplus.c b/grub-core/fs/hfsplus.c
index 1c7791b02..361e5be49 100644
--- a/grub-core/fs/hfsplus.c
+++ b/grub-core/fs/hfsplus.c
@@ -177,6 +177,17 @@ grub_hfsplus_read_block (grub_fshelp_node_t node, grub_disk_addr_t fileblock)
 	  break;
 	}
 
+      /*
+       * If the extent overflow tree isn't ready yet, we can't look
+       * in it. This can happen where the catalog file is corrupted.
+       */
+      if (!node->data->extoverflow_tree_ready)
+	{
+	  grub_error (GRUB_ERR_BAD_FS,
+		      "attempted to read extent overflow tree before loading");
+	  break;
+	}
+
       /* Set up the key to look for in the extent overflow file.  */
       extoverflow.extkey.fileid = node->fileid;
       extoverflow.extkey.type = 0;
@@ -241,6 +252,7 @@ grub_hfsplus_mount (grub_disk_t disk)
     return 0;
 
   data->disk = disk;
+  data->extoverflow_tree_ready = 0;
 
   /* Read the bootblock.  */
   grub_disk_read (disk, GRUB_HFSPLUS_SBLOCK, 0, sizeof (volheader),
@@ -357,6 +369,8 @@ grub_hfsplus_mount (grub_disk_t disk)
   if (data->extoverflow_tree.nodesize < 2)
     goto fail;
 
+  data->extoverflow_tree_ready = 1;
+
   if (grub_hfsplus_read_file (&data->attr_tree.file, 0, 0,
 			      sizeof (struct grub_hfsplus_btnode),
 			      sizeof (header), (char *) &header) <= 0)
diff --git a/include/grub/hfsplus.h b/include/grub/hfsplus.h
index 117740ae2..e14dd31ff 100644
--- a/include/grub/hfsplus.h
+++ b/include/grub/hfsplus.h
@@ -113,6 +113,8 @@ struct grub_hfsplus_data
   struct grub_hfsplus_btree extoverflow_tree;
   struct grub_hfsplus_btree attr_tree;
 
+  int extoverflow_tree_ready;
+
   struct grub_hfsplus_file dirroot;
   struct grub_hfsplus_file opened_file;