diff --git a/src/crypto/x509/parser.go b/src/crypto/x509/parser.go
index f085162a4e88be..9a500a8098ca8f 100644
--- a/src/crypto/x509/parser.go
+++ b/src/crypto/x509/parser.go
@@ -51,9 +51,9 @@ func isPrintable(b byte) bool {
 }
 
 // parseASN1String parses the ASN.1 string types T61String, PrintableString,
-// UTF8String, BMPString, and IA5String. This is mostly copied from the
-// respective encoding/asn1.parse... methods, rather than just increasing
-// the API surface of that package.
+// UTF8String, BMPString, IA5String, and NumericString. This is mostly copied
+// from the respective encoding/asn1.parse... methods, rather than just
+// increasing the API surface of that package.
 func parseASN1String(tag cryptobyte_asn1.Tag, value []byte) (string, error) {
 	switch tag {
 	case cryptobyte_asn1.T61String:
@@ -93,6 +93,13 @@ func parseASN1String(tag cryptobyte_asn1.Tag, value []byte) (string, error) {
 			return "", errors.New("invalid IA5String")
 		}
 		return s, nil
+	case cryptobyte_asn1.Tag(asn1.TagNumericString):
+		for _, b := range value {
+			if !('0' <= b && b <= '9' || b == ' ') {
+				return "", errors.New("invalid NumericString")
+			}
+		}
+		return string(value), nil
 	}
 	return "", fmt.Errorf("unsupported string type: %v", tag)
 }
diff --git a/src/crypto/x509/parser_test.go b/src/crypto/x509/parser_test.go
new file mode 100644
index 00000000000000..d7cf7ea758a5e6
--- /dev/null
+++ b/src/crypto/x509/parser_test.go
@@ -0,0 +1,102 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+package x509
+
+import (
+	"encoding/asn1"
+	"testing"
+
+	cryptobyte_asn1 "golang.org/x/crypto/cryptobyte/asn1"
+)
+
+func TestParseASN1String(t *testing.T) {
+	tests := []struct {
+		name        string
+		tag         cryptobyte_asn1.Tag
+		value       []byte
+		expected    string
+		expectedErr string
+	}{
+		{
+			name:     "T61String",
+			tag:      cryptobyte_asn1.T61String,
+			value:    []byte{80, 81, 82},
+			expected: string("PQR"),
+		},
+		{
+			name:     "PrintableString",
+			tag:      cryptobyte_asn1.PrintableString,
+			value:    []byte{80, 81, 82},
+			expected: string("PQR"),
+		},
+		{
+			name:        "PrintableString (invalid)",
+			tag:         cryptobyte_asn1.PrintableString,
+			value:       []byte{1, 2, 3},
+			expectedErr: "invalid PrintableString",
+		},
+		{
+			name:     "UTF8String",
+			tag:      cryptobyte_asn1.UTF8String,
+			value:    []byte{80, 81, 82},
+			expected: string("PQR"),
+		},
+		{
+			name:        "UTF8String (invalid)",
+			tag:         cryptobyte_asn1.UTF8String,
+			value:       []byte{255},
+			expectedErr: "invalid UTF-8 string",
+		},
+		{
+			name:     "BMPString",
+			tag:      cryptobyte_asn1.Tag(asn1.TagBMPString),
+			value:    []byte{80, 81},
+			expected: string("偑"),
+		},
+		{
+			name:        "BMPString (invalid length)",
+			tag:         cryptobyte_asn1.Tag(asn1.TagBMPString),
+			value:       []byte{255},
+			expectedErr: "invalid BMPString",
+		},
+		{
+			name:     "IA5String",
+			tag:      cryptobyte_asn1.IA5String,
+			value:    []byte{80, 81},
+			expected: string("PQ"),
+		},
+		{
+			name:        "IA5String (invalid)",
+			tag:         cryptobyte_asn1.IA5String,
+			value:       []byte{255},
+			expectedErr: "invalid IA5String",
+		},
+		{
+			name:     "NumericString",
+			tag:      cryptobyte_asn1.Tag(asn1.TagNumericString),
+			value:    []byte{49, 50},
+			expected: string("12"),
+		},
+		{
+			name:        "NumericString (invalid)",
+			tag:         cryptobyte_asn1.Tag(asn1.TagNumericString),
+			value:       []byte{80},
+			expectedErr: "invalid NumericString",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			out, err := parseASN1String(tc.tag, tc.value)
+			if err != nil && err.Error() != tc.expectedErr {
+				t.Fatalf("parseASN1String returned unexpected error: got %q, want %q", err, tc.expectedErr)
+			} else if err == nil && tc.expectedErr != "" {
+				t.Fatalf("parseASN1String didn't fail, expected: %s", tc.expectedErr)
+			}
+			if out != tc.expected {
+				t.Fatalf("parseASN1String returned unexpected value: got %q, want %q", out, tc.expected)
+			}
+		})
+	}
+}