diff --git a/jhalfs b/jhalfs
index 37ce1ae..2173eb2 100755
--- a/jhalfs
+++ b/jhalfs
@@ -81,6 +81,18 @@ Options:
 help="\
 Try '$0 --help' for more information."
 
+no_empty_builddir="\
+echo \"\" >&2
+echo \"        W A R N I N G\" >&2
+echo \"\" >&2
+echo \"Look like the \$BUILDDIR directory contains subdirectories\" >&2
+echo \"from a previous LFS build.\" >&2
+echo \"\" >&2
+echo \"Please, format the partition mounted on \$BUILDDIR or set\" >&2
+echo \"a diferent build directory before to run jhalfs.\" >&2
+echo \"\" >&2
+exit 1"
+
 exit_missing_arg="\
 echo \"Option '\$1' requires an argument\" >&2
 echo \"\$help\" >&2
@@ -90,7 +102,6 @@ no_dl_client="\
 echo \"Could not find a way to download the LFS sources.\" >&2
 echo \"Attempting to continue.\" >&2"
 
-
 HEADER="# This file is automatically generated by jhalfs
 # DO NOT EDIT THIS FILE MANUALLY
 #
@@ -1009,6 +1020,14 @@ while test $# -gt 0 ; do
   shift
 done
 
+# If $BUILDDIR have subdirectories like tools/ or bin/, stop the run
+# and notify the user about that. This also prevent to set "-d /"
+# by mistake.
+
+if [ -d $BUILDDIR/tools -o -d $BUILDDIR/bin ] ; then
+  eval "$no_empty_builddir"
+fi
+
 # Find the download client to use, if not already specified.
 
 if [ -z $DL ] ; then