diff --git a/syndicate.sh b/syndicate.sh
index 63436fa..0e4109f 100755
--- a/syndicate.sh
+++ b/syndicate.sh
@@ -1,5 +1,7 @@
 #!/bin/bash
 
+set -euo pipefail
+
 ds_handle=0
 ds_buf=""
 declare -A ds_handles
@@ -65,7 +67,7 @@ ds_assert() {
     local h="$ds_handle"
     ds_handle=$(($ds_handle + 1))
     ds_action "$1" "<assert $2 $h>"
-    if [ -n "$3" ]
+    if [ -n "${3:-}" ]
     then
         ds_handle_oids[$3]="$1"
         ds_handles[$3]="$h"