diff --git a/backup.sh b/backup.sh
index dac6c76..7165c68 100755
--- a/backup.sh
+++ b/backup.sh
@@ -36,7 +36,7 @@ SNAPSHOT_DATASETS=""
 
 debug()
 {
-    if [ -z $BG_DEBUG_MODE -or ! $BG_DEBUG_MODE = "TRUE" ]; then
+    if [ -z $BG_DEBUG_MODE -o $BG_DEBUG_MODE != "TRUE" ]; then
         :
     else
         echo $@