diff --git a/pkg/textparse/openmetricsparse.go b/pkg/textparse/openmetricsparse.go
index 853076f1d..708ae5dd9 100644
--- a/pkg/textparse/openmetricsparse.go
+++ b/pkg/textparse/openmetricsparse.go
@@ -20,7 +20,6 @@ import (
 	"io"
 	"math"
 	"sort"
-	"strconv"
 	"strings"
 	"unicode/utf8"
 
@@ -268,7 +267,7 @@ func (p *OpenMetricsParser) Next() (Entry, error) {
 		if t2 != tValue {
 			return EntryInvalid, parseError("expected value after metric", t)
 		}
-		if p.val, err = strconv.ParseFloat(yoloString(p.l.buf()[1:]), 64); err != nil {
+		if p.val, err = parseFloat(yoloString(p.l.buf()[1:])); err != nil {
 			return EntryInvalid, err
 		}
 		// Ensure canonical NaN value.
@@ -283,7 +282,7 @@ func (p *OpenMetricsParser) Next() (Entry, error) {
 			p.hasTS = true
 			var ts float64
 			// A float is enough to hold what we need for millisecond resolution.
-			if ts, err = strconv.ParseFloat(yoloString(p.l.buf()[1:]), 64); err != nil {
+			if ts, err = parseFloat(yoloString(p.l.buf()[1:])); err != nil {
 				return EntryInvalid, err
 			}
 			p.ts = int64(ts * 1000)
diff --git a/pkg/textparse/openmetricsparse_test.go b/pkg/textparse/openmetricsparse_test.go
index f8c792588..6bb6bdfab 100644
--- a/pkg/textparse/openmetricsparse_test.go
+++ b/pkg/textparse/openmetricsparse_test.go
@@ -370,6 +370,22 @@ func TestOpenMetricsParseErrors(t *testing.T) {
 			input: "empty_label_name{=\"\"} 0",
 			err:   "expected label name or left brace, got \"EQUAL\"",
 		},
+		{
+			input: "foo 1_2\n",
+			err:   "unsupported character in float",
+		},
+		{
+			input: "foo 0x1p-3\n",
+			err:   "unsupported character in float",
+		},
+		{
+			input: "foo 0x1P-3\n",
+			err:   "unsupported character in float",
+		},
+		{
+			input: "foo 0 1_2\n",
+			err:   "unsupported character in float",
+		},
 	}
 
 	for i, c := range cases {
diff --git a/pkg/textparse/promparse.go b/pkg/textparse/promparse.go
index f05b87abd..2ecb04bff 100644
--- a/pkg/textparse/promparse.go
+++ b/pkg/textparse/promparse.go
@@ -332,7 +332,7 @@ func (p *PromParser) Next() (Entry, error) {
 		if t2 != tValue {
 			return EntryInvalid, parseError("expected value after metric", t)
 		}
-		if p.val, err = strconv.ParseFloat(yoloString(p.l.buf()), 64); err != nil {
+		if p.val, err = parseFloat(yoloString(p.l.buf())); err != nil {
 			return EntryInvalid, err
 		}
 		// Ensure canonical NaN value.
@@ -409,3 +409,11 @@ var helpReplacer = strings.NewReplacer(
 func yoloString(b []byte) string {
 	return *((*string)(unsafe.Pointer(&b)))
 }
+
+func parseFloat(s string) (float64, error) {
+	// Keep to pre-Go 1.13 float formats.
+	if strings.ContainsAny(s, "pP_") {
+		return 0, fmt.Errorf("unsupported character in float")
+	}
+	return strconv.ParseFloat(s, 64)
+}
diff --git a/pkg/textparse/promparse_test.go b/pkg/textparse/promparse_test.go
index 7bfa36fc0..9b62079d5 100644
--- a/pkg/textparse/promparse_test.go
+++ b/pkg/textparse/promparse_test.go
@@ -249,6 +249,22 @@ func TestPromParseErrors(t *testing.T) {
 			input: "empty_label_name{=\"\"} 0",
 			err:   "expected label name, got \"EQUAL\"",
 		},
+		{
+			input: "foo 1_2\n",
+			err:   "unsupported character in float",
+		},
+		{
+			input: "foo 0x1p-3\n",
+			err:   "unsupported character in float",
+		},
+		{
+			input: "foo 0x1P-3\n",
+			err:   "unsupported character in float",
+		},
+		{
+			input: "foo 0 1_2\n",
+			err:   "expected next entry after timestamp, got \"MNAME\"",
+		},
 	}
 
 	for i, c := range cases {