diff --git a/powerwall.sh b/powerwall.sh
index 80db5a97..6e2b1271 100755
--- a/powerwall.sh
+++ b/powerwall.sh
@@ -52,7 +52,7 @@ CHECKTEMP_SERVICE(){
 				echo ${TEMP_THRESHOLDS[${1}]} | cut -d',' -f 1 | read temp_warn
 				echo ${TEMP_THRESHOLDS[${1}]} | cut -d',' -f 2 | read temp_crit
 				
-				temp_diff=$(($last_temp%.* - $temp_f%.*))
+				temp_diff=$((${last_temp%.*} - ${temp_f%.*}))
 				[ $temp_diff -lt 0 ] && temp_diff=$(($temp_diff * -1))
 						
 				if [ $(bc -l <<< "$temp_f >= $temp_warn") -eq 1 ] && [ $(bc -l <<< "$temp_f < $temp_crit") -eq 1 ]; then