diff --git a/init/do_mounts.c b/init/do_mounts.c
index 3715feb8446d5c84796310e975d4948fd88df9ea..d055b1914c3d3b696237a04bb352ed5dbb7e14c6 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -263,6 +263,10 @@ void __init mount_block_root(char *name, int flags)
 		printk("Please append a correct \"root=\" boot option; here are the available partitions:\n");
 
 		printk_all_partitions();
+#ifdef CONFIG_DEBUG_BLOCK_EXT_DEVT
+		printk("DEBUG_BLOCK_EXT_DEVT is enabled, you need to specify "
+		       "explicit textual name for \"root=\" boot option.\n");
+#endif
 		panic("VFS: Unable to mount root fs on %s", b);
 	}
 
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 4378d5e923ca25e55ed229b6dc106f1ceb834d85..c556896abe57e9680295899cb1f681122d260f4e 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -638,6 +638,12 @@ config DEBUG_BLOCK_EXT_DEVT
 	  userland code paths which assume predetermined contiguous
 	  device number allocation.
 
+	  Note that turning on this debug option shuffles all the
+	  device numbers for all IDE and SCSI devices including libata
+	  ones, so root partition specified using device number
+	  directly (via rdev or root=MAJ:MIN) won't work anymore.
+	  Textual device names (root=/dev/sdXn) will continue to work.
+
 	  Say N if you are unsure.
 
 config LKDTM