diff --git a/build-aux/update-subdirs b/build-aux/update-subdirs
index 336029fb710..96712f0b32e 100755
--- a/build-aux/update-subdirs
+++ b/build-aux/update-subdirs
@@ -26,7 +26,7 @@ for file in *; do
 	*.elc | *.el | term | RCS | CVS | Old | . | .. | =* | *~ | *.orig | *.rej)
 	  ;;
 	*)
-	    if [ -d $file ]; then
+            if [ -d "$file" ]; then
 		if [ "$file" = "obsolete" ]; then
 		    subdirs="$subdirs \"$file\""
 		else