diff --git a/bootstrap.sh b/bootstrap.sh
index 5dfe5e9044..bfdc9c77eb 100755
--- a/bootstrap.sh
+++ b/bootstrap.sh
@@ -241,7 +241,7 @@ the headers only.
 
 The Boost libraries requiring separate building and installation are:
 EOF
-  $BJAM -d0 --show-libraries | grep '^\s*-'
+  $BJAM -d0 --show-libraries | grep '^[[:space:]]*-'
   exit 0
 fi