diff --git a/tools/build-ardour-stack b/tools/build-ardour-stack
index 0c5d969360..122e28fa68 100755
--- a/tools/build-ardour-stack
+++ b/tools/build-ardour-stack
@@ -36,7 +36,7 @@ while [ $# -gt 0 ] ; do
 done
 
 
-if [ $clean -o $makespace ] ; then
+if [ x$clean != x -o x$makespace != x ] ; then
     if [ ! -d LRDF ] ; then 
         echo "This doesn't appear to be your source directory. Don't run --clean or --space here."
         exit 1
diff --git a/tools/build-gtk-stack b/tools/build-gtk-stack
index 2263d1c862..21bd9ccb5e 100755
--- a/tools/build-gtk-stack
+++ b/tools/build-gtk-stack
@@ -45,7 +45,7 @@ while [ $# -gt 0 ] ; do
     esac
 done
 
-if [ $clean -o $makespace ] ; then
+if [ x$clean != x -o x$makespace != x ] ; then
     if [ ! -d gtk+ ] ; then 
         echo "This doesn't appear to be your source directory. Don't run --clean or --space here."
         exit 1