diff --git a/check-env-temp.sh b/check-env-temp.sh
index 4fc0d5d..acc2d97 100644
--- a/check-env-temp.sh
+++ b/check-env-temp.sh
@@ -89,7 +89,13 @@ script_name=$(basename "${0}")
 script_dir=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
 GetOptions "$@"
 
-val=$(temper --json | jq '.[0]."internal temperature"' | bc -l)
+json=$(temper --json)
+if [[ ${json} == '[]' ]]; then
+    echo "MEMORY UNKNOWN - Temper USB not found"
+    exit 3
+fi
+
+val=$(echo ${json} | jq '.[0]."internal temperature"' | bc -l)
 
 if (( $(echo "$val < ${critmin}" | bc -l) )); then
     rval=2