diff --git a/mackerel-plugin-snmp/lib/snmp.go b/mackerel-plugin-snmp/lib/snmp.go
index 8df2f694b..326ff4560 100644
--- a/mackerel-plugin-snmp/lib/snmp.go
+++ b/mackerel-plugin-snmp/lib/snmp.go
@@ -52,8 +52,17 @@ func (m SNMPPlugin) FetchMetrics() (map[string]interface{}, error) {
 
 		ret, err := strconv.ParseFloat(fmt.Sprint(resp.Variables[0].Value), 64)
 		if err != nil {
-			log.Println(err)
-			continue
+			// NOTE: Cannot assume strconv.ParseFloat("%s", resp.Variables[0].Value)
+			// first, as resp.Variables[0].Value may be an int class, etc.
+			// Normally, an object values such as INTEGER or Counter are
+			// successfully accepted in the above conversions.
+			// However, STRING object values are passed as byte arrays, so the above
+			// conversion will result in an error.
+			ret, err = strconv.ParseFloat(fmt.Sprintf("%s", resp.Variables[0].Value), 64)
+			if err != nil {
+				log.Println(err)
+				continue
+			}
 		}
 
 		stat[sm.Metrics.Name] = ret
diff --git a/mackerel-plugin-snmp/rule.txt b/mackerel-plugin-snmp/rule.txt
index 247e6b2a4..8c83ff471 100644
--- a/mackerel-plugin-snmp/rule.txt
+++ b/mackerel-plugin-snmp/rule.txt
@@ -1,2 +1,3 @@
 snmp.hrSystemNumUsers	>=0
 snmp.hrSystemProcesses	>=0
+snmp.echo	>0
diff --git a/mackerel-plugin-snmp/test.sh b/mackerel-plugin-snmp/test.sh
index 6062a129b..22f3ec5cb 100755
--- a/mackerel-plugin-snmp/test.sh
+++ b/mackerel-plugin-snmp/test.sh
@@ -26,7 +26,7 @@ docker run --name "test-$plugin" -v $(pwd)/testdata/snmpd.conf:/etc/snmp/snmpd.c
 trap 'docker stop test-$plugin; docker rm test-$plugin; exit 1' 1 2 3 15
 sleep 10
 
-$plugin '.1.3.6.1.2.1.25.1.5.0:hrSystemNumUsers:0:0' '.1.3.6.1.2.1.25.1.6.0:hrSystemProcesses:0:0' | graphite-metric-test -f rule.txt
+$plugin '.1.3.6.1.2.1.25.1.5.0:hrSystemNumUsers:0:0' '.1.3.6.1.2.1.25.1.6.0:hrSystemProcesses:0:0' '.1.3.6.1.4.1.8072.1.3.2.3.1.2.4.101.99.104.111:echo:0:0' | graphite-metric-test -f rule.txt
 status=$?
 
 docker stop "test-$plugin"
diff --git a/mackerel-plugin-snmp/testdata/snmpd.conf b/mackerel-plugin-snmp/testdata/snmpd.conf
index 9238dc279..4dbf6298d 100644
--- a/mackerel-plugin-snmp/testdata/snmpd.conf
+++ b/mackerel-plugin-snmp/testdata/snmpd.conf
@@ -1,4 +1,7 @@
-view   systemonly  included   .1.3.6.1.2.1.1
-view   systemonly  included   .1.3.6.1.2.1.25.1
-
-rocommunity public  default    -V systemonly
+view   systemonly  included   .1.3.6.1.2.1.1
+view   systemonly  included   .1.3.6.1.2.1.25.1
+view   systemonly  included   .1.3.6.1.4.1.8072.1.3.2.3.1.2.4
+
+rocommunity public  default    -V systemonly
+
+extend echo /bin/echo '3.14'