diff --git a/scripts/poky-env-internal b/scripts/poky-env-internal
index e1797a06c2..81b1425489 100755
--- a/scripts/poky-env-internal
+++ b/scripts/poky-env-internal
@@ -40,7 +40,7 @@ MSG=''
 unset BDIR
 
 BUILD_ARCH=`uname -m`
-BUILD_OS=`uname | tr [A-Z] [a-z]`
+BUILD_OS=`uname | tr '[A-Z]' '[a-z]'`
 BUILD_SYS="$BUILD_ARCH-$BUILD_OS"
 
 PATH="$BBDIR/bin/:$OEROOT/scripts:$PATH"