diff --git a/common/json/context.go b/common/json/context.go
index b68d5711..7a490704 100644
--- a/common/json/context.go
+++ b/common/json/context.go
@@ -1,4 +1,4 @@
-//go:build go1.21 && !without_contextjson
+//go:build go1.20 && !without_contextjson
 
 package json
 
diff --git a/common/json/internal/contextjson/encode.go b/common/json/internal/contextjson/encode.go
index 6da0bd9c..296177a5 100644
--- a/common/json/internal/contextjson/encode.go
+++ b/common/json/internal/contextjson/encode.go
@@ -442,7 +442,7 @@ func marshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	b, err := m.MarshalJSON()
 	if err == nil {
 		e.Grow(len(b))
-		out := e.AvailableBuffer()
+		out := availableBuffer(&e.Buffer)
 		out, err = appendCompact(out, b, opts.escapeHTML)
 		e.Buffer.Write(out)
 	}
@@ -461,7 +461,7 @@ func addrMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	b, err := m.MarshalJSON()
 	if err == nil {
 		e.Grow(len(b))
-		out := e.AvailableBuffer()
+		out := availableBuffer(&e.Buffer)
 		out, err = appendCompact(out, b, opts.escapeHTML)
 		e.Buffer.Write(out)
 	}
@@ -484,7 +484,7 @@ func textMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	if err != nil {
 		e.error(&MarshalerError{v.Type(), err, "MarshalText"})
 	}
-	e.Write(appendString(e.AvailableBuffer(), b, opts.escapeHTML))
+	e.Write(appendString(availableBuffer(&e.Buffer), b, opts.escapeHTML))
 }
 
 func addrTextMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
@@ -498,11 +498,11 @@ func addrTextMarshalerEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	if err != nil {
 		e.error(&MarshalerError{v.Type(), err, "MarshalText"})
 	}
-	e.Write(appendString(e.AvailableBuffer(), b, opts.escapeHTML))
+	e.Write(appendString(availableBuffer(&e.Buffer), b, opts.escapeHTML))
 }
 
 func boolEncoder(e *encodeState, v reflect.Value, opts encOpts) {
-	b := e.AvailableBuffer()
+	b := availableBuffer(&e.Buffer)
 	b = mayAppendQuote(b, opts.quoted)
 	b = strconv.AppendBool(b, v.Bool())
 	b = mayAppendQuote(b, opts.quoted)
@@ -510,7 +510,7 @@ func boolEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 }
 
 func intEncoder(e *encodeState, v reflect.Value, opts encOpts) {
-	b := e.AvailableBuffer()
+	b := availableBuffer(&e.Buffer)
 	b = mayAppendQuote(b, opts.quoted)
 	b = strconv.AppendInt(b, v.Int(), 10)
 	b = mayAppendQuote(b, opts.quoted)
@@ -518,7 +518,7 @@ func intEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 }
 
 func uintEncoder(e *encodeState, v reflect.Value, opts encOpts) {
-	b := e.AvailableBuffer()
+	b := availableBuffer(&e.Buffer)
 	b = mayAppendQuote(b, opts.quoted)
 	b = strconv.AppendUint(b, v.Uint(), 10)
 	b = mayAppendQuote(b, opts.quoted)
@@ -538,7 +538,7 @@ func (bits floatEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
 	// See golang.org/issue/6384 and golang.org/issue/14135.
 	// Like fmt %g, but the exponent cutoffs are different
 	// and exponents themselves are not padded to two digits.
-	b := e.AvailableBuffer()
+	b := availableBuffer(&e.Buffer)
 	b = mayAppendQuote(b, opts.quoted)
 	abs := math.Abs(f)
 	fmt := byte('f')
@@ -577,7 +577,7 @@ func stringEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 		if !isValidNumber(numStr) {
 			e.error(fmt.Errorf("json: invalid number literal %q", numStr))
 		}
-		b := e.AvailableBuffer()
+		b := availableBuffer(&e.Buffer)
 		b = mayAppendQuote(b, opts.quoted)
 		b = append(b, numStr...)
 		b = mayAppendQuote(b, opts.quoted)
@@ -586,9 +586,9 @@ func stringEncoder(e *encodeState, v reflect.Value, opts encOpts) {
 	}
 	if opts.quoted {
 		b := appendString(nil, v.String(), opts.escapeHTML)
-		e.Write(appendString(e.AvailableBuffer(), b, false)) // no need to escape again since it is already escaped
+		e.Write(appendString(availableBuffer(&e.Buffer), b, false)) // no need to escape again since it is already escaped
 	} else {
-		e.Write(appendString(e.AvailableBuffer(), v.String(), opts.escapeHTML))
+		e.Write(appendString(availableBuffer(&e.Buffer), v.String(), opts.escapeHTML))
 	}
 }
 
@@ -754,7 +754,7 @@ func (me mapEncoder) encode(e *encodeState, v reflect.Value, opts encOpts) {
 		if i > 0 {
 			e.WriteByte(',')
 		}
-		e.Write(appendString(e.AvailableBuffer(), kv.ks, opts.escapeHTML))
+		e.Write(appendString(availableBuffer(&e.Buffer), kv.ks, opts.escapeHTML))
 		e.WriteByte(':')
 		me.elemEnc(e, kv.v, opts)
 	}
@@ -786,7 +786,7 @@ func encodeByteSlice(e *encodeState, v reflect.Value, _ encOpts) {
 	e.Grow(len(`"`) + encodedLen + len(`"`))
 
 	// TODO(https://go.dev/issue/53693): Use base64.Encoding.AppendEncode.
-	b := e.AvailableBuffer()
+	b := availableBuffer(&e.Buffer)
 	b = append(b, '"')
 	base64.StdEncoding.Encode(b[len(b):][:encodedLen], s)
 	b = b[:len(b)+encodedLen]
diff --git a/common/json/internal/contextjson/indent.go b/common/json/internal/contextjson/indent.go
index 26bb5d2e..99951208 100644
--- a/common/json/internal/contextjson/indent.go
+++ b/common/json/internal/contextjson/indent.go
@@ -6,6 +6,11 @@ package json
 
 import "bytes"
 
+// TODO(https://go.dev/issue/53685): Use bytes.Buffer.AvailableBuffer instead.
+func availableBuffer(b *bytes.Buffer) []byte {
+	return b.Bytes()[b.Len():]
+}
+
 // HTMLEscape appends to dst the JSON-encoded src with <, >, &, U+2028 and U+2029
 // characters inside string literals changed to \u003c, \u003e, \u0026, \u2028, \u2029
 // so that the JSON will be safe to embed inside HTML <script> tags.
@@ -13,7 +18,7 @@ import "bytes"
 // escaping within <script> tags, so an alternative JSON encoding must be used.
 func HTMLEscape(dst *bytes.Buffer, src []byte) {
 	dst.Grow(len(src))
-	dst.Write(appendHTMLEscape(dst.AvailableBuffer(), src))
+	dst.Write(appendHTMLEscape(availableBuffer(dst), src))
 }
 
 func appendHTMLEscape(dst, src []byte) []byte {
@@ -40,7 +45,7 @@ func appendHTMLEscape(dst, src []byte) []byte {
 // insignificant space characters elided.
 func Compact(dst *bytes.Buffer, src []byte) error {
 	dst.Grow(len(src))
-	b := dst.AvailableBuffer()
+	b := availableBuffer(dst)
 	b, err := appendCompact(b, src, false)
 	dst.Write(b)
 	return err
@@ -109,7 +114,7 @@ const indentGrowthFactor = 2
 // if src ends in a trailing newline, so will dst.
 func Indent(dst *bytes.Buffer, src []byte, prefix, indent string) error {
 	dst.Grow(indentGrowthFactor * len(src))
-	b := dst.AvailableBuffer()
+	b := availableBuffer(dst)
 	b, err := appendIndent(b, src, prefix, indent)
 	dst.Write(b)
 	return err
diff --git a/common/json/std.go b/common/json/std.go
index e9280dcf..22612458 100644
--- a/common/json/std.go
+++ b/common/json/std.go
@@ -1,4 +1,4 @@
-//go:build !go1.21 || without_contextjson
+//go:build !go1.20 || without_contextjson
 
 package json