diff --git a/internal/encoding/text/encode.go b/internal/encoding/text/encode.go
index 19dbcb0..6320fe2 100644
--- a/internal/encoding/text/encode.go
+++ b/internal/encoding/text/encode.go
@@ -124,7 +124,7 @@
 			// are used to represent both the proto string and bytes type.
 			r = rune(in[0])
 			fallthrough
-		case r < ' ' || r == '"' || r == '\\':
+		case r < ' ' || r == '"' || r == '\\' || r == 0x7f:
 			out = append(out, '\\')
 			switch r {
 			case '"', '\\':
@@ -166,7 +166,7 @@
 // escaping. If no characters need escaping, this returns the input length.
 func indexNeedEscapeInString(s string) int {
 	for i := 0; i < len(s); i++ {
-		if c := s[i]; c < ' ' || c == '"' || c == '\'' || c == '\\' || c >= utf8.RuneSelf {
+		if c := s[i]; c < ' ' || c == '"' || c == '\'' || c == '\\' || c >= 0x7f {
 			return i
 		}
 	}
diff --git a/internal/encoding/text/encode_test.go b/internal/encoding/text/encode_test.go
index 2588b1b..6a65883 100644
--- a/internal/encoding/text/encode_test.go
+++ b/internal/encoding/text/encode_test.go
@@ -403,8 +403,8 @@
 				}
 				return string(b)
 			}(),
-			wantOut:      `"\x01\x02\x03\x04\x05\x06\x07\x08\t\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !\"#$%&()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]^_` + "`abcdefghijklmnopqrstuvwxyz{|}~\x7f\"",
-			wantOutASCII: `"\x01\x02\x03\x04\x05\x06\x07\x08\t\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !\"#$%&()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]^_` + "`abcdefghijklmnopqrstuvwxyz{|}~\x7f\"",
+			wantOut:      `"\x01\x02\x03\x04\x05\x06\x07\x08\t\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !\"#$%&()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]^_` + "`abcdefghijklmnopqrstuvwxyz{|}~\\x7f\"",
+			wantOutASCII: `"\x01\x02\x03\x04\x05\x06\x07\x08\t\x0b\x0c\r\x0e\x0f\x10\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !\"#$%&()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]^_` + "`abcdefghijklmnopqrstuvwxyz{|}~\\x7f\"",
 		},
 		{
 			// Valid UTF-8 wire encoding of the RuneError rune.
@@ -483,6 +483,11 @@
 			wantOutASCII: `"\x0f"`,
 		},
 		{
+			in:           "\x7f",
+			wantOut:      `"\x7f"`,
+			wantOutASCII: `"\x7f"`,
+		},
+		{
 			in:           "\xff",
 			wantOut:      `"\xff"`,
 			wantOutASCII: `"\xff"`,