diff --git a/agent/accumulator.go b/agent/accumulator.go
index b04ff2b53..7ec22cd7f 100644
--- a/agent/accumulator.go
+++ b/agent/accumulator.go
@@ -105,7 +105,6 @@ func (ac *accumulator) AddFields(
 				continue
 			}
 		}
-		result[k] = v
 
 		// Validate uint64 and float64 fields
 		switch val := v.(type) {
@@ -116,6 +115,7 @@ func (ac *accumulator) AddFields(
 			} else {
 				result[k] = int64(9223372036854775807)
 			}
+			continue
 		case float64:
 			// NaNs are invalid values in influxdb, skip measurement
 			if math.IsNaN(val) || math.IsInf(val, 0) {
@@ -127,6 +127,8 @@ func (ac *accumulator) AddFields(
 				continue
 			}
 		}
+
+		result[k] = v
 	}
 	fields = nil
 	if len(result) == 0 {
@@ -168,5 +170,8 @@ func (ac *accumulator) setDefaultTags(tags map[string]string) {
 }
 
 func (ac *accumulator) addDefaultTag(key, value string) {
+	if ac.defaultTags == nil {
+		ac.defaultTags = make(map[string]string)
+	}
 	ac.defaultTags[key] = value
 }
diff --git a/agent/accumulator_test.go b/agent/accumulator_test.go
new file mode 100644
index 000000000..05f9b02aa
--- /dev/null
+++ b/agent/accumulator_test.go
@@ -0,0 +1,302 @@
+package agent
+
+import (
+	"fmt"
+	"math"
+	"testing"
+	"time"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/internal/models"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestAdd(t *testing.T) {
+	a := accumulator{}
+	now := time.Now()
+	a.metrics = make(chan telegraf.Metric, 10)
+	defer close(a.metrics)
+	a.inputConfig = &internal_models.InputConfig{}
+
+	a.Add("acctest", float64(101), map[string]string{})
+	a.Add("acctest", float64(101), map[string]string{"acc": "test"})
+	a.Add("acctest", float64(101), map[string]string{"acc": "test"}, now)
+
+	testm := <-a.metrics
+	actual := testm.String()
+	assert.Contains(t, actual, "acctest value=101")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Contains(t, actual, "acctest,acc=test value=101")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Equal(t,
+		fmt.Sprintf("acctest,acc=test value=101 %d", now.UnixNano()),
+		actual)
+}
+
+func TestAddDefaultTags(t *testing.T) {
+	a := accumulator{}
+	a.addDefaultTag("default", "tag")
+	now := time.Now()
+	a.metrics = make(chan telegraf.Metric, 10)
+	defer close(a.metrics)
+	a.inputConfig = &internal_models.InputConfig{}
+
+	a.Add("acctest", float64(101), map[string]string{})
+	a.Add("acctest", float64(101), map[string]string{"acc": "test"})
+	a.Add("acctest", float64(101), map[string]string{"acc": "test"}, now)
+
+	testm := <-a.metrics
+	actual := testm.String()
+	assert.Contains(t, actual, "acctest,default=tag value=101")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Contains(t, actual, "acctest,acc=test,default=tag value=101")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Equal(t,
+		fmt.Sprintf("acctest,acc=test,default=tag value=101 %d", now.UnixNano()),
+		actual)
+}
+
+func TestAddFields(t *testing.T) {
+	a := accumulator{}
+	now := time.Now()
+	a.metrics = make(chan telegraf.Metric, 10)
+	defer close(a.metrics)
+	a.inputConfig = &internal_models.InputConfig{}
+
+	fields := map[string]interface{}{
+		"usage": float64(99),
+	}
+	a.AddFields("acctest", fields, map[string]string{})
+	a.AddFields("acctest", fields, map[string]string{"acc": "test"})
+	a.AddFields("acctest", fields, map[string]string{"acc": "test"}, now)
+
+	testm := <-a.metrics
+	actual := testm.String()
+	assert.Contains(t, actual, "acctest usage=99")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Contains(t, actual, "acctest,acc=test usage=99")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Equal(t,
+		fmt.Sprintf("acctest,acc=test usage=99 %d", now.UnixNano()),
+		actual)
+}
+
+// Test that all Inf fields get dropped, and not added to metrics channel
+func TestAddInfFields(t *testing.T) {
+	inf := math.Inf(1)
+	ninf := math.Inf(-1)
+
+	a := accumulator{}
+	now := time.Now()
+	a.metrics = make(chan telegraf.Metric, 10)
+	defer close(a.metrics)
+	a.inputConfig = &internal_models.InputConfig{}
+
+	fields := map[string]interface{}{
+		"usage":  inf,
+		"nusage": ninf,
+	}
+	a.AddFields("acctest", fields, map[string]string{})
+	a.AddFields("acctest", fields, map[string]string{"acc": "test"})
+	a.AddFields("acctest", fields, map[string]string{"acc": "test"}, now)
+
+	assert.Len(t, a.metrics, 0)
+
+	// test that non-inf fields are kept and not dropped
+	fields["notinf"] = float64(100)
+	a.AddFields("acctest", fields, map[string]string{})
+	testm := <-a.metrics
+	actual := testm.String()
+	assert.Contains(t, actual, "acctest notinf=100")
+}
+
+// Test that nan fields are dropped and not added
+func TestAddNaNFields(t *testing.T) {
+	nan := math.NaN()
+
+	a := accumulator{}
+	now := time.Now()
+	a.metrics = make(chan telegraf.Metric, 10)
+	defer close(a.metrics)
+	a.inputConfig = &internal_models.InputConfig{}
+
+	fields := map[string]interface{}{
+		"usage": nan,
+	}
+	a.AddFields("acctest", fields, map[string]string{})
+	a.AddFields("acctest", fields, map[string]string{"acc": "test"})
+	a.AddFields("acctest", fields, map[string]string{"acc": "test"}, now)
+
+	assert.Len(t, a.metrics, 0)
+
+	// test that non-nan fields are kept and not dropped
+	fields["notnan"] = float64(100)
+	a.AddFields("acctest", fields, map[string]string{})
+	testm := <-a.metrics
+	actual := testm.String()
+	assert.Contains(t, actual, "acctest notnan=100")
+}
+
+func TestAddUint64Fields(t *testing.T) {
+	a := accumulator{}
+	now := time.Now()
+	a.metrics = make(chan telegraf.Metric, 10)
+	defer close(a.metrics)
+	a.inputConfig = &internal_models.InputConfig{}
+
+	fields := map[string]interface{}{
+		"usage": uint64(99),
+	}
+	a.AddFields("acctest", fields, map[string]string{})
+	a.AddFields("acctest", fields, map[string]string{"acc": "test"})
+	a.AddFields("acctest", fields, map[string]string{"acc": "test"}, now)
+
+	testm := <-a.metrics
+	actual := testm.String()
+	assert.Contains(t, actual, "acctest usage=99i")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Contains(t, actual, "acctest,acc=test usage=99i")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Equal(t,
+		fmt.Sprintf("acctest,acc=test usage=99i %d", now.UnixNano()),
+		actual)
+}
+
+func TestAddUint64Overflow(t *testing.T) {
+	a := accumulator{}
+	now := time.Now()
+	a.metrics = make(chan telegraf.Metric, 10)
+	defer close(a.metrics)
+	a.inputConfig = &internal_models.InputConfig{}
+
+	fields := map[string]interface{}{
+		"usage": uint64(9223372036854775808),
+	}
+	a.AddFields("acctest", fields, map[string]string{})
+	a.AddFields("acctest", fields, map[string]string{"acc": "test"})
+	a.AddFields("acctest", fields, map[string]string{"acc": "test"}, now)
+
+	testm := <-a.metrics
+	actual := testm.String()
+	assert.Contains(t, actual, "acctest usage=9223372036854775807i")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Contains(t, actual, "acctest,acc=test usage=9223372036854775807i")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Equal(t,
+		fmt.Sprintf("acctest,acc=test usage=9223372036854775807i %d", now.UnixNano()),
+		actual)
+}
+
+func TestAddInts(t *testing.T) {
+	a := accumulator{}
+	a.addDefaultTag("default", "tag")
+	now := time.Now()
+	a.metrics = make(chan telegraf.Metric, 10)
+	defer close(a.metrics)
+	a.inputConfig = &internal_models.InputConfig{}
+
+	a.Add("acctest", int(101), map[string]string{})
+	a.Add("acctest", int32(101), map[string]string{"acc": "test"})
+	a.Add("acctest", int64(101), map[string]string{"acc": "test"}, now)
+
+	testm := <-a.metrics
+	actual := testm.String()
+	assert.Contains(t, actual, "acctest,default=tag value=101i")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Contains(t, actual, "acctest,acc=test,default=tag value=101i")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Equal(t,
+		fmt.Sprintf("acctest,acc=test,default=tag value=101i %d", now.UnixNano()),
+		actual)
+}
+
+func TestAddFloats(t *testing.T) {
+	a := accumulator{}
+	a.addDefaultTag("default", "tag")
+	now := time.Now()
+	a.metrics = make(chan telegraf.Metric, 10)
+	defer close(a.metrics)
+	a.inputConfig = &internal_models.InputConfig{}
+
+	a.Add("acctest", float32(101), map[string]string{"acc": "test"})
+	a.Add("acctest", float64(101), map[string]string{"acc": "test"}, now)
+
+	testm := <-a.metrics
+	actual := testm.String()
+	assert.Contains(t, actual, "acctest,acc=test,default=tag value=101")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Equal(t,
+		fmt.Sprintf("acctest,acc=test,default=tag value=101 %d", now.UnixNano()),
+		actual)
+}
+
+func TestAddStrings(t *testing.T) {
+	a := accumulator{}
+	a.addDefaultTag("default", "tag")
+	now := time.Now()
+	a.metrics = make(chan telegraf.Metric, 10)
+	defer close(a.metrics)
+	a.inputConfig = &internal_models.InputConfig{}
+
+	a.Add("acctest", "test", map[string]string{"acc": "test"})
+	a.Add("acctest", "foo", map[string]string{"acc": "test"}, now)
+
+	testm := <-a.metrics
+	actual := testm.String()
+	assert.Contains(t, actual, "acctest,acc=test,default=tag value=\"test\"")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Equal(t,
+		fmt.Sprintf("acctest,acc=test,default=tag value=\"foo\" %d", now.UnixNano()),
+		actual)
+}
+
+func TestAddBools(t *testing.T) {
+	a := accumulator{}
+	a.addDefaultTag("default", "tag")
+	now := time.Now()
+	a.metrics = make(chan telegraf.Metric, 10)
+	defer close(a.metrics)
+	a.inputConfig = &internal_models.InputConfig{}
+
+	a.Add("acctest", true, map[string]string{"acc": "test"})
+	a.Add("acctest", false, map[string]string{"acc": "test"}, now)
+
+	testm := <-a.metrics
+	actual := testm.String()
+	assert.Contains(t, actual, "acctest,acc=test,default=tag value=true")
+
+	testm = <-a.metrics
+	actual = testm.String()
+	assert.Equal(t,
+		fmt.Sprintf("acctest,acc=test,default=tag value=false %d", now.UnixNano()),
+		actual)
+}