diff --git a/src/pkg/bytes/bytes_test.go b/src/pkg/bytes/bytes_test.go
index 55aa0a065c6..ce3f37e4de2 100644
--- a/src/pkg/bytes/bytes_test.go
+++ b/src/pkg/bytes/bytes_test.go
@@ -829,7 +829,7 @@ var ReplaceTests = []ReplaceTest{
 
 func TestReplace(t *testing.T) {
 	for _, tt := range ReplaceTests {
-		in := append([]byte(tt.in), []byte("<spare>")...)
+		in := append([]byte(tt.in), "<spare>"...)
 		in = in[:len(tt.in)]
 		out := Replace(in, []byte(tt.old), []byte(tt.new), tt.n)
 		if s := string(out); s != tt.out {
diff --git a/src/pkg/exp/norm/normregtest.go b/src/pkg/exp/norm/normregtest.go
index 3c17741d204..cbd73ffa759 100644
--- a/src/pkg/exp/norm/normregtest.go
+++ b/src/pkg/exp/norm/normregtest.go
@@ -280,7 +280,7 @@ func PerformanceTest() {
 	success := make(chan bool, 1)
 	go func() {
 		buf := bytes.Repeat([]byte("\u035D"), 1024*1024)
-		buf = append(buf, []byte("\u035B")...)
+		buf = append(buf, "\u035B"...)
 		norm.NFC.Append(nil, buf...)
 		success <- true
 	}()
diff --git a/src/pkg/exp/norm/readwriter_test.go b/src/pkg/exp/norm/readwriter_test.go
index b415f2b8cc0..68652efa65b 100644
--- a/src/pkg/exp/norm/readwriter_test.go
+++ b/src/pkg/exp/norm/readwriter_test.go
@@ -23,7 +23,7 @@ var bufSizes = []int{1, 2, 3, 4, 5, 6, 7, 8, 100, 101, 102, 103, 4000, 4001, 400
 
 func readFunc(size int) appendFunc {
 	return func(f Form, out []byte, s string) []byte {
-		out = append(out, []byte(s)...)
+		out = append(out, s...)
 		r := f.Reader(bytes.NewBuffer(out))
 		buf := make([]byte, size)
 		result := []byte{}
@@ -46,7 +46,7 @@ func TestReader(t *testing.T) {
 
 func writeFunc(size int) appendFunc {
 	return func(f Form, out []byte, s string) []byte {
-		in := append(out, []byte(s)...)
+		in := append(out, s...)
 		result := new(bytes.Buffer)
 		w := f.Writer(result)
 		buf := make([]byte, size)
diff --git a/src/pkg/exp/ssh/messages.go b/src/pkg/exp/ssh/messages.go
index def294543c6..851c89747dd 100644
--- a/src/pkg/exp/ssh/messages.go
+++ b/src/pkg/exp/ssh/messages.go
@@ -323,7 +323,7 @@ func marshal(msgType uint8, msg interface{}) []byte {
 			out = append(out, byte(len(s)>>16))
 			out = append(out, byte(len(s)>>8))
 			out = append(out, byte(len(s)))
-			out = append(out, []byte(s)...)
+			out = append(out, s...)
 		case reflect.Slice:
 			switch t.Elem().Kind() {
 			case reflect.Uint8:
@@ -354,7 +354,7 @@ func marshal(msgType uint8, msg interface{}) []byte {
 					if j != 0 {
 						out = append(out, ',')
 					}
-					out = append(out, []byte(field.Index(j).String())...)
+					out = append(out, field.Index(j).String()...)
 				}
 			default:
 				panic("slice of unknown type")
diff --git a/src/pkg/json/scanner_test.go b/src/pkg/json/scanner_test.go
index 404cbd0ea9d..4d73eac8aaa 100644
--- a/src/pkg/json/scanner_test.go
+++ b/src/pkg/json/scanner_test.go
@@ -175,7 +175,7 @@ func TestNextValueBig(t *testing.T) {
 		t.Errorf("invalid rest: %d", len(rest))
 	}
 
-	item, rest, err = nextValue(append(jsonBig, []byte("HELLO WORLD")...), &scan)
+	item, rest, err = nextValue(append(jsonBig, "HELLO WORLD"...), &scan)
 	if err != nil {
 		t.Fatalf("nextValue extra: %s", err)
 	}
diff --git a/src/pkg/os/dir_plan9.go b/src/pkg/os/dir_plan9.go
index bbc2cb64726..bf17005dd5c 100644
--- a/src/pkg/os/dir_plan9.go
+++ b/src/pkg/os/dir_plan9.go
@@ -295,6 +295,6 @@ func pstring(b []byte, s string) []byte {
 		panic(NewError("string too long"))
 	}
 	b = pbit16(b, uint16(len(s)))
-	b = append(b, []byte(s)...)
+	b = append(b, s...)
 	return b
 }
diff --git a/src/pkg/os/env.go b/src/pkg/os/env.go
index 3772c090b8f..4844fa3e26d 100644
--- a/src/pkg/os/env.go
+++ b/src/pkg/os/env.go
@@ -16,9 +16,9 @@ func Expand(s string, mapping func(string) string) string {
 	i := 0
 	for j := 0; j < len(s); j++ {
 		if s[j] == '$' && j+1 < len(s) {
-			buf = append(buf, []byte(s[i:j])...)
+			buf = append(buf, s[i:j]...)
 			name, w := getShellName(s[j+1:])
-			buf = append(buf, []byte(mapping(name))...)
+			buf = append(buf, mapping(name)...)
 			j += w
 			i = j + 1
 		}