diff --git a/plugins/inputs/exec/exec.go b/plugins/inputs/exec/exec.go
index ae13081bf..cd34d7954 100644
--- a/plugins/inputs/exec/exec.go
+++ b/plugins/inputs/exec/exec.go
@@ -19,6 +19,7 @@ import (
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/config"
 	"github.com/influxdata/telegraf/internal"
+	"github.com/influxdata/telegraf/models"
 	"github.com/influxdata/telegraf/plugins/inputs"
 	"github.com/influxdata/telegraf/plugins/parsers"
 	"github.com/influxdata/telegraf/plugins/parsers/nagios"
@@ -29,16 +30,22 @@ var sampleConfig string
 
 const MaxStderrBytes int = 512
 
+type exitcodeHandlerFunc func([]telegraf.Metric, error, []byte) []telegraf.Metric
+
 type Exec struct {
 	Commands    []string        `toml:"commands"`
 	Command     string          `toml:"command"`
 	Environment []string        `toml:"environment"`
 	Timeout     config.Duration `toml:"timeout"`
+	Log         telegraf.Logger `toml:"-"`
 
 	parser parsers.Parser
 
 	runner Runner
-	Log    telegraf.Logger `toml:"-"`
+
+	// Allow post processing of command exit codes
+	exitcodeHandler   exitcodeHandlerFunc
+	parseDespiteError bool
 }
 
 func NewExec() *Exec {
@@ -134,10 +141,9 @@ func (*Exec) SampleConfig() string {
 
 func (e *Exec) ProcessCommand(command string, acc telegraf.Accumulator, wg *sync.WaitGroup) {
 	defer wg.Done()
-	_, isNagios := e.parser.(*nagios.Parser)
 
 	out, errBuf, runErr := e.runner.Run(command, e.Environment, time.Duration(e.Timeout))
-	if !isNagios && runErr != nil {
+	if !e.parseDespiteError && runErr != nil {
 		err := fmt.Errorf("exec: %s for command '%s': %s", runErr, command, string(errBuf))
 		acc.AddError(err)
 		return
@@ -149,8 +155,8 @@ func (e *Exec) ProcessCommand(command string, acc telegraf.Accumulator, wg *sync
 		return
 	}
 
-	if isNagios {
-		metrics = nagios.AddState(runErr, errBuf, metrics)
+	if e.exitcodeHandler != nil {
+		metrics = e.exitcodeHandler(metrics, runErr, errBuf)
 	}
 
 	for _, m := range metrics {
@@ -160,6 +166,13 @@ func (e *Exec) ProcessCommand(command string, acc telegraf.Accumulator, wg *sync
 
 func (e *Exec) SetParser(parser parsers.Parser) {
 	e.parser = parser
+	unwrapped, ok := parser.(*models.RunningParser)
+	if ok {
+		if _, ok := unwrapped.Parser.(*nagios.Parser); ok {
+			e.exitcodeHandler = nagiosHandler
+			e.parseDespiteError = true
+		}
+	}
 }
 
 func (e *Exec) Gather(acc telegraf.Accumulator) error {
@@ -213,6 +226,10 @@ func (e *Exec) Init() error {
 	return nil
 }
 
+func nagiosHandler(metrics []telegraf.Metric, err error, msg []byte) []telegraf.Metric {
+	return nagios.AddState(err, msg, metrics)
+}
+
 func init() {
 	inputs.Add("exec", func() telegraf.Input {
 		return NewExec()
diff --git a/plugins/inputs/execd/execd.go b/plugins/inputs/execd/execd.go
index 63f3179c0..813379875 100644
--- a/plugins/inputs/execd/execd.go
+++ b/plugins/inputs/execd/execd.go
@@ -13,10 +13,10 @@ import (
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/config"
 	"github.com/influxdata/telegraf/internal/process"
+	"github.com/influxdata/telegraf/models"
 	"github.com/influxdata/telegraf/plugins/inputs"
 	"github.com/influxdata/telegraf/plugins/parsers"
 	"github.com/influxdata/telegraf/plugins/parsers/influx"
-	"github.com/influxdata/telegraf/plugins/parsers/prometheus"
 )
 
 //go:embed sample.conf
@@ -29,9 +29,10 @@ type Execd struct {
 	RestartDelay config.Duration `toml:"restart_delay"`
 	Log          telegraf.Logger `toml:"-"`
 
-	process *process.Process
-	acc     telegraf.Accumulator
-	parser  parsers.Parser
+	process      *process.Process
+	acc          telegraf.Accumulator
+	parser       parsers.Parser
+	outputReader func(io.Reader)
 }
 
 func (*Execd) SampleConfig() string {
@@ -40,6 +41,14 @@ func (*Execd) SampleConfig() string {
 
 func (e *Execd) SetParser(parser parsers.Parser) {
 	e.parser = parser
+	e.outputReader = e.cmdReadOut
+
+	unwrapped, ok := parser.(*models.RunningParser)
+	if ok {
+		if _, ok := unwrapped.Parser.(*influx.Parser); ok {
+			e.outputReader = e.cmdReadOutStream
+		}
+	}
 }
 
 func (e *Execd) Start(acc telegraf.Accumulator) error {
@@ -51,7 +60,7 @@ func (e *Execd) Start(acc telegraf.Accumulator) error {
 	}
 	e.process.Log = e.Log
 	e.process.RestartDelay = time.Duration(e.RestartDelay)
-	e.process.ReadStdoutFn = e.cmdReadOut
+	e.process.ReadStdoutFn = e.outputReader
 	e.process.ReadStderrFn = e.cmdReadErr
 
 	if err = e.process.Start(); err != nil {
@@ -73,22 +82,10 @@ func (e *Execd) Stop() {
 }
 
 func (e *Execd) cmdReadOut(out io.Reader) {
-	if _, isInfluxParser := e.parser.(*influx.Parser); isInfluxParser {
-		// work around the lack of built-in streaming parser. :(
-		e.cmdReadOutStream(out)
-		return
-	}
-
-	_, isPrometheus := e.parser.(*prometheus.Parser)
-
 	scanner := bufio.NewScanner(out)
 
 	for scanner.Scan() {
 		data := scanner.Bytes()
-		if isPrometheus {
-			data = append(data, []byte("\n")...)
-		}
-
 		metrics, err := e.parser.Parse(data)
 		if err != nil {
 			e.acc.AddError(fmt.Errorf("parse error: %w", err))
diff --git a/plugins/inputs/execd/execd_test.go b/plugins/inputs/execd/execd_test.go
index 500107e4d..45879551f 100644
--- a/plugins/inputs/execd/execd_test.go
+++ b/plugins/inputs/execd/execd_test.go
@@ -17,6 +17,7 @@ import (
 	"github.com/influxdata/telegraf/metric"
 	"github.com/influxdata/telegraf/models"
 	"github.com/influxdata/telegraf/plugins/parsers/influx"
+	"github.com/influxdata/telegraf/plugins/parsers/prometheus"
 	"github.com/influxdata/telegraf/plugins/serializers"
 	"github.com/influxdata/telegraf/testutil"
 )
@@ -42,7 +43,7 @@ func TestSettingConfigWorks(t *testing.T) {
 }
 
 func TestExternalInputWorks(t *testing.T) {
-	influxParser := &influx.Parser{}
+	influxParser := models.NewRunningParser(&influx.Parser{}, &models.ParserConfig{})
 	require.NoError(t, influxParser.Init())
 
 	exe, err := os.Executable()
@@ -52,10 +53,10 @@ func TestExternalInputWorks(t *testing.T) {
 		Command:      []string{exe, "-counter"},
 		Environment:  []string{"PLUGINS_INPUTS_EXECD_MODE=application", "METRIC_NAME=counter"},
 		RestartDelay: config.Duration(5 * time.Second),
-		parser:       influxParser,
 		Signal:       "STDIN",
 		Log:          testutil.Logger{},
 	}
+	e.SetParser(influxParser)
 
 	metrics := make(chan telegraf.Metric, 10)
 	defer close(metrics)
@@ -76,7 +77,7 @@ func TestExternalInputWorks(t *testing.T) {
 }
 
 func TestParsesLinesContainingNewline(t *testing.T) {
-	parser := &influx.Parser{}
+	parser := models.NewRunningParser(&influx.Parser{}, &models.ParserConfig{})
 	require.NoError(t, parser.Init())
 
 	metrics := make(chan telegraf.Metric, 10)
@@ -85,11 +86,11 @@ func TestParsesLinesContainingNewline(t *testing.T) {
 
 	e := &Execd{
 		RestartDelay: config.Duration(5 * time.Second),
-		parser:       parser,
 		Signal:       "STDIN",
 		acc:          acc,
 		Log:          testutil.Logger{},
 	}
+	e.SetParser(parser)
 
 	cases := []struct {
 		Name  string
@@ -108,7 +109,7 @@ func TestParsesLinesContainingNewline(t *testing.T) {
 		t.Run(test.Name, func(t *testing.T) {
 			line := fmt.Sprintf("event message=\"%v\" 1587128639239000000", test.Value)
 
-			e.cmdReadOut(strings.NewReader(line))
+			e.outputReader(strings.NewReader(line))
 
 			m := readChanWithTimeout(t, metrics, 1*time.Second)
 
@@ -120,6 +121,43 @@ func TestParsesLinesContainingNewline(t *testing.T) {
 	}
 }
 
+func TestParsesPrometheus(t *testing.T) {
+	parser := models.NewRunningParser(&prometheus.Parser{}, &models.ParserConfig{})
+	require.NoError(t, parser.Init())
+
+	metrics := make(chan telegraf.Metric, 10)
+	defer close(metrics)
+
+	var acc testutil.Accumulator
+
+	e := &Execd{
+		RestartDelay: config.Duration(5 * time.Second),
+		Signal:       "STDIN",
+		acc:          &acc,
+		Log:          testutil.Logger{},
+	}
+	e.SetParser(parser)
+
+	lines := `# HELP This is just a test metric.
+# TYPE test summary
+test{handler="execd",quantile="0.5"} 42.0
+`
+	expected := []telegraf.Metric{
+		testutil.MustMetric(
+			"prometheus",
+			map[string]string{"handler": "execd", "quantile": "0.5"},
+			map[string]interface{}{"test": float64(42.0)},
+			time.Unix(0, 0),
+		),
+	}
+
+	e.outputReader(strings.NewReader(lines))
+	check := func() bool { return acc.NMetrics() == uint64(len(expected)) }
+	require.Eventually(t, check, 1*time.Second, 100*time.Millisecond)
+	actual := acc.GetTelegrafMetrics()
+	testutil.RequireMetricsEqual(t, expected, actual, testutil.IgnoreTime())
+}
+
 func readChanWithTimeout(t *testing.T, metrics chan telegraf.Metric, timeout time.Duration) telegraf.Metric {
 	to := time.NewTimer(timeout)
 	defer to.Stop()
diff --git a/plugins/parsers/prometheus/parser.go b/plugins/parsers/prometheus/parser.go
index fb34311f2..c4b03d8e9 100644
--- a/plugins/parsers/prometheus/parser.go
+++ b/plugins/parsers/prometheus/parser.go
@@ -30,8 +30,13 @@ func (p *Parser) Parse(buf []byte) ([]telegraf.Metric, error) {
 	var parser expfmt.TextParser
 	var metrics []telegraf.Metric
 	var err error
-	// parse even if the buffer begins with a newline
+
+	// Make sure we have a finishing newline but no trailing one
 	buf = bytes.TrimPrefix(buf, []byte("\n"))
+	if !bytes.HasSuffix(buf, []byte("\n")) {
+		buf = append(buf, []byte("\n")...)
+	}
+
 	// Read raw data
 	buffer := bytes.NewBuffer(buf)
 	reader := bufio.NewReader(buffer)