diff --git a/nagios/check_diskstats.sh b/nagios/check_diskstats.sh
index 32273bf..dc691b7 100755
--- a/nagios/check_diskstats.sh
+++ b/nagios/check_diskstats.sh
@@ -71,6 +71,7 @@ fi
 while getopts hd:i:I: OPT; do
 	case "$OPT" in
 		'd')
+			DEVICE_FOUND=0
 			while read \
 				MAJOR MINOR DEVICE_NAME \
 				READS_COMPLETED READS_MERGED SECTORS_READ TIME_SPENT_READING \
@@ -83,6 +84,7 @@ while getopts hd:i:I: OPT; do
 			do
 				case "$DEVICE_NAME" in
 					$OPTARG)
+						DEVICE_FOUND=1
 						# Checking the thresholds
 						if [ -n "$THRESHOLD_IO_IN_PROGRESS_CRITICAL" ] && [ "$IO_IN_PROGRESS" -gt "$THRESHOLD_IO_IN_PROGRESS_CRITICAL" ]; then
 							OUTPUT_EXIT_STATUS=$STATE_CRITICAL
@@ -117,6 +119,16 @@ while getopts hd:i:I: OPT; do
 						;;
 				esac
 			done < /proc/diskstats
+			# Check if the device requested has been found.
+			if [ "$DEVICE_FOUND" -lt 1 ]; then
+				echo "UNKNOWN device '$OPTARG' not found."
+				exit $STATE_UNKNOWN
+			fi
+			;;
+
+		'h')
+			usage
+			exit 0
 			;;
 
 		'i')
@@ -134,6 +146,8 @@ while getopts hd:i:I: OPT; do
 	esac
 done
 
+# Should we check if no device has been requested ? Overkill ?
+
 # Final ouput
 case "$OUTPUT_EXIT_STATUS" in
 	'0')