diff --git a/src/cmd/goyacc/goyacc.go b/src/cmd/goyacc/goyacc.go
index 63e287a9a54..c9fa6bfb96f 100644
--- a/src/cmd/goyacc/goyacc.go
+++ b/src/cmd/goyacc/goyacc.go
@@ -3139,7 +3139,7 @@ out:
 		c = yyTok2[1] /* unknown char */
 	}
 	if yyDebug >= 3 {
-		fmt.Printf("lex %.4x %s\n", uint(yychar), yyTokname(c))
+		fmt.Printf("lex %U %s\n", uint(yychar), yyTokname(c))
 	}
 	return c
 }
diff --git a/src/pkg/bytes/buffer_test.go b/src/pkg/bytes/buffer_test.go
index 2801ad10fd3..ef42d430cbb 100644
--- a/src/pkg/bytes/buffer_test.go
+++ b/src/pkg/bytes/buffer_test.go
@@ -275,10 +275,10 @@ func TestRuneIO(t *testing.T) {
 		size := utf8.EncodeRune(b[n:], r)
 		nbytes, err := buf.WriteRune(r)
 		if err != nil {
-			t.Fatalf("WriteRune(U+%.4x) error: %s", r, err)
+			t.Fatalf("WriteRune(%U) error: %s", r, err)
 		}
 		if nbytes != size {
-			t.Fatalf("WriteRune(U+%.4x) expected %d, got %d", r, size, nbytes)
+			t.Fatalf("WriteRune(%U) expected %d, got %d", r, size, nbytes)
 		}
 		n += size
 	}
@@ -295,7 +295,7 @@ func TestRuneIO(t *testing.T) {
 		size := utf8.EncodeRune(p, r)
 		nr, nbytes, err := buf.ReadRune()
 		if nr != r || nbytes != size || err != nil {
-			t.Fatalf("ReadRune(U+%.4x) got U+%.4x,%d not U+%.4x,%d (err=%s)", r, nr, nbytes, r, size, err)
+			t.Fatalf("ReadRune(%U) got %U,%d not %U,%d (err=%s)", r, nr, nbytes, r, size, err)
 		}
 	}
 
@@ -305,11 +305,11 @@ func TestRuneIO(t *testing.T) {
 	for r := 0; r < NRune; r++ {
 		r1, size, _ := buf.ReadRune()
 		if err := buf.UnreadRune(); err != nil {
-			t.Fatalf("UnreadRune(U+%.4x) got error %q", r, err)
+			t.Fatalf("UnreadRune(%U) got error %q", r, err)
 		}
 		r2, nbytes, err := buf.ReadRune()
 		if r1 != r2 || r1 != r || nbytes != size || err != nil {
-			t.Fatalf("ReadRune(U+%.4x) after UnreadRune got U+%.4x,%d not U+%.4x,%d (err=%s)", r, r2, nbytes, r, size, err)
+			t.Fatalf("ReadRune(%U) after UnreadRune got %U,%d not %U,%d (err=%s)", r, r2, nbytes, r, size, err)
 		}
 	}
 }
diff --git a/src/pkg/unicode/maketables.go b/src/pkg/unicode/maketables.go
index 65a55de9d5d..4c6d83f3e69 100644
--- a/src/pkg/unicode/maketables.go
+++ b/src/pkg/unicode/maketables.go
@@ -157,7 +157,7 @@ func parseCategory(line string) (state State) {
 	char := &chars[point]
 	char.field = field
 	if char.codePoint != 0 {
-		die.Logf("point U+%04x reused\n")
+		die.Logf("point %U reused\n")
 	}
 	char.codePoint = lastChar
 	char.category = field[FGeneralCategory]
@@ -167,7 +167,7 @@ func parseCategory(line string) (state State) {
 		// Decimal digit
 		_, err := strconv.Atoi(field[FNumericValue])
 		if err != nil {
-			die.Log("U+%04x: bad numeric field: %s", point, err)
+			die.Log("%U: bad numeric field: %s", point, err)
 		}
 	case "Lu":
 		char.letter(field[FCodePoint], field[FSimpleLowercaseMapping], field[FSimpleTitlecaseMapping])
@@ -208,7 +208,7 @@ func (char *Char) letterValue(s string, cas string) int {
 	v, err := strconv.Btoui64(s, 16)
 	if err != nil {
 		char.dump(cas)
-		die.Logf("U+%04x: bad letter(%s): %s", char.codePoint, s, err)
+		die.Logf("%U: bad letter(%s): %s", char.codePoint, s, err)
 	}
 	return int(v)
 }
diff --git a/src/pkg/utf8/string_test.go b/src/pkg/utf8/string_test.go
index 484d46fbffd..0733b061c16 100644
--- a/src/pkg/utf8/string_test.go
+++ b/src/pkg/utf8/string_test.go
@@ -21,7 +21,7 @@ func TestScanForwards(t *testing.T) {
 		for i, expect := range runes {
 			got := str.At(i)
 			if got != expect {
-				t.Errorf("%s[%d]: expected %c (U+%04x); got %c (U+%04x)", s, i, expect, expect, got, got)
+				t.Errorf("%s[%d]: expected %c (%U); got %c (%U)", s, i, expect, expect, got, got)
 			}
 		}
 	}
@@ -39,7 +39,7 @@ func TestScanBackwards(t *testing.T) {
 			expect := runes[i]
 			got := str.At(i)
 			if got != expect {
-				t.Errorf("%s[%d]: expected %c (U+%04x); got %c (U+%04x)", s, i, expect, expect, got, got)
+				t.Errorf("%s[%d]: expected %c (%U); got %c (%U)", s, i, expect, expect, got, got)
 			}
 		}
 	}
@@ -63,7 +63,7 @@ func TestRandomAccess(t *testing.T) {
 			expect := runes[i]
 			got := str.At(i)
 			if got != expect {
-				t.Errorf("%s[%d]: expected %c (U+%04x); got %c (U+%04x)", s, i, expect, expect, got, got)
+				t.Errorf("%s[%d]: expected %c (%U); got %c (%U)", s, i, expect, expect, got, got)
 			}
 		}
 	}
diff --git a/src/pkg/utf8/utf8_test.go b/src/pkg/utf8/utf8_test.go
index ecaf2d872a4..59896aa656d 100644
--- a/src/pkg/utf8/utf8_test.go
+++ b/src/pkg/utf8/utf8_test.go
@@ -58,11 +58,11 @@ func TestFullRune(t *testing.T) {
 		m := utf8map[i]
 		b := []byte(m.str)
 		if !FullRune(b) {
-			t.Errorf("FullRune(%q) (rune %04x) = false, want true", b, m.rune)
+			t.Errorf("FullRune(%q) (%U) = false, want true", b, m.rune)
 		}
 		s := m.str
 		if !FullRuneInString(s) {
-			t.Errorf("FullRuneInString(%q) (rune %04x) = false, want true", s, m.rune)
+			t.Errorf("FullRuneInString(%q) (%U) = false, want true", s, m.rune)
 		}
 		b1 := b[0 : len(b)-1]
 		if FullRune(b1) {
@@ -172,7 +172,7 @@ func TestIntConversion(t *testing.T) {
 		i := 0
 		for _, r := range ts {
 			if r != runes[i] {
-				t.Errorf("%q[%d]: expected %c (U+%04x); got %c (U+%04x)", ts, i, runes[i], runes[i], r, r)
+				t.Errorf("%q[%d]: expected %c (%U); got %c (%U)", ts, i, runes[i], runes[i], r, r)
 			}
 			i++
 		}