diff --git a/src/cmd/compile/internal/syntax/nodes_test.go b/src/cmd/compile/internal/syntax/nodes_test.go
index 1bba9eeacf..433ae30661 100644
--- a/src/cmd/compile/internal/syntax/nodes_test.go
+++ b/src/cmd/compile/internal/syntax/nodes_test.go
@@ -290,8 +290,8 @@ func testPos(t *testing.T, list []test, prefix, suffix string, extract func(*Fil
 			continue
 		}
 
-		// build syntaxt tree
-		file, err := ParseBytes(nil, []byte(src), nil, nil, nil, 0)
+		// build syntax tree
+		file, err := Parse(nil, strings.NewReader(src), nil, nil, nil, 0)
 		if err != nil {
 			t.Errorf("parse error: %s: %v (%s)", src, err, test.nodetyp)
 			continue
diff --git a/src/cmd/compile/internal/syntax/parser_test.go b/src/cmd/compile/internal/syntax/parser_test.go
index 309f1333f4..684a8429af 100644
--- a/src/cmd/compile/internal/syntax/parser_test.go
+++ b/src/cmd/compile/internal/syntax/parser_test.go
@@ -131,7 +131,7 @@ func verifyPrint(filename string, ast1 *File) {
 		panic(err)
 	}
 
-	ast2, err := ParseBytes(src.NewFileBase(filename, filename), buf1.Bytes(), nil, nil, nil, 0)
+	ast2, err := Parse(src.NewFileBase(filename, filename), &buf1, nil, nil, nil, 0)
 	if err != nil {
 		panic(err)
 	}
@@ -155,7 +155,7 @@ func verifyPrint(filename string, ast1 *File) {
 }
 
 func TestIssue17697(t *testing.T) {
-	_, err := ParseBytes(nil, nil, nil, nil, nil, 0) // return with parser error, don't panic
+	_, err := Parse(nil, bytes.NewReader(nil), nil, nil, nil, 0) // return with parser error, don't panic
 	if err == nil {
 		t.Errorf("no error reported")
 	}
@@ -208,7 +208,7 @@ func TestLineDirectives(t *testing.T) {
 			}
 			return name
 		}
-		_, err := ParseBytes(nil, []byte(test.src), nil, nil, fileh, 0)
+		_, err := Parse(nil, strings.NewReader(test.src), nil, nil, fileh, 0)
 		if err == nil {
 			t.Errorf("%s: no error reported", test.src)
 			continue
diff --git a/src/cmd/compile/internal/syntax/printer_test.go b/src/cmd/compile/internal/syntax/printer_test.go
index bbf75a957d..c218924202 100644
--- a/src/cmd/compile/internal/syntax/printer_test.go
+++ b/src/cmd/compile/internal/syntax/printer_test.go
@@ -7,6 +7,7 @@ package syntax
 import (
 	"fmt"
 	"os"
+	"strings"
 	"testing"
 )
 
@@ -29,7 +30,7 @@ func TestPrintString(t *testing.T) {
 		"package p; type _ = int; type T1 = struct{}; type ( _ = *struct{}; T2 = float32 )",
 		// TODO(gri) expand
 	} {
-		ast, err := ParseBytes(nil, []byte(want), nil, nil, nil, 0)
+		ast, err := Parse(nil, strings.NewReader(want), nil, nil, nil, 0)
 		if err != nil {
 			t.Error(err)
 			continue
diff --git a/src/cmd/compile/internal/syntax/scanner_test.go b/src/cmd/compile/internal/syntax/scanner_test.go
index 53995e0c79..ba4ba8f69c 100644
--- a/src/cmd/compile/internal/syntax/scanner_test.go
+++ b/src/cmd/compile/internal/syntax/scanner_test.go
@@ -5,6 +5,7 @@
 package syntax
 
 import (
+	"bytes"
 	"fmt"
 	"os"
 	"strings"
@@ -42,17 +43,17 @@ func TestScanner(t *testing.T) {
 
 func TestTokens(t *testing.T) {
 	// make source
-	var buf []byte
+	var buf bytes.Buffer
 	for i, s := range sampleTokens {
-		buf = append(buf, "\t\t\t\t"[:i&3]...)     // leading indentation
-		buf = append(buf, s.src...)                // token
-		buf = append(buf, "        "[:i&7]...)     // trailing spaces
-		buf = append(buf, "/* foo */ // bar\n"...) // comments
+		buf.WriteString("\t\t\t\t"[:i&3])     // leading indentation
+		buf.WriteString(s.src)                // token
+		buf.WriteString("        "[:i&7])     // trailing spaces
+		buf.WriteString("/* foo */ // bar\n") // comments
 	}
 
 	// scan source
 	var got scanner
-	got.init(&bytesReader{buf}, nil, nil)
+	got.init(&buf, nil, nil)
 	got.next()
 	for i, want := range sampleTokens {
 		nlsemi := false
@@ -337,7 +338,7 @@ func TestScanErrors(t *testing.T) {
 	} {
 		var s scanner
 		nerrors := 0
-		s.init(&bytesReader{[]byte(test.src)}, func(line, col uint, msg string) {
+		s.init(strings.NewReader(test.src), func(line, col uint, msg string) {
 			nerrors++
 			// only check the first error
 			if nerrors == 1 {
diff --git a/src/cmd/compile/internal/syntax/syntax.go b/src/cmd/compile/internal/syntax/syntax.go
index f58d5efd29..f6e9303290 100644
--- a/src/cmd/compile/internal/syntax/syntax.go
+++ b/src/cmd/compile/internal/syntax/syntax.go
@@ -57,12 +57,11 @@ type FilenameHandler func(name string) string
 // process as much source as possible. If errh is nil, Parse will terminate
 // immediately upon encountering an error.
 //
-// If a PragmaHandler is provided, it is called with each pragma encountered.
+// If pragh != nil, it is called with each pragma encountered.
 //
-// If a FilenameHandler is provided, it is called to process each filename
+// If fileh != nil, it is called to process each filename
 // encountered in //line directives.
 //
-// The Mode argument is currently ignored.
 func Parse(base *src.PosBase, src io.Reader, errh ErrorHandler, pragh PragmaHandler, fileh FilenameHandler, mode Mode) (_ *File, first error) {
 	defer func() {
 		if p := recover(); p != nil {
@@ -80,24 +79,6 @@ func Parse(base *src.PosBase, src io.Reader, errh ErrorHandler, pragh PragmaHand
 	return p.fileOrNil(), p.first
 }
 
-// ParseBytes behaves like Parse but it reads the source from the []byte slice provided.
-func ParseBytes(base *src.PosBase, src []byte, errh ErrorHandler, pragh PragmaHandler, fileh FilenameHandler, mode Mode) (*File, error) {
-	return Parse(base, &bytesReader{src}, errh, pragh, fileh, mode)
-}
-
-type bytesReader struct {
-	data []byte
-}
-
-func (r *bytesReader) Read(p []byte) (int, error) {
-	if len(r.data) > 0 {
-		n := copy(p, r.data)
-		r.data = r.data[n:]
-		return n, nil
-	}
-	return 0, io.EOF
-}
-
 // ParseFile behaves like Parse but it reads the source from the named file.
 func ParseFile(filename string, errh ErrorHandler, pragh PragmaHandler, mode Mode) (*File, error) {
 	f, err := os.Open(filename)