diff --git a/common.quota b/common.quota
index 77368a55..a00b832e 100644
--- a/common.quota
+++ b/common.quota
@@ -90,7 +90,7 @@ _choose_gid()
 
 _choose_prid()
 {
-    if [ $projid_file == "" ]; then
+    if [ "X$projid_file" == "X" ]; then
 	projid_file=/etc/projid
     fi
     if [ ! -f $projid_file ]; then