diff --git a/src/runtime/debug/stack.go b/src/runtime/debug/stack.go
index ab12bff..952d834 100644
--- a/src/runtime/debug/stack.go
+++ b/src/runtime/debug/stack.go
@@ -7,92 +7,26 @@
 package debug
 
 import (
-	"bytes"
-	"fmt"
-	"io/ioutil"
 	"os"
 	"runtime"
 )
 
-var (
-	dunno     = []byte("???")
-	centerDot = []byte("·")
-	dot       = []byte(".")
-	slash     = []byte("/")
-)
-
 // PrintStack prints to standard error the stack trace returned by Stack.
 func PrintStack() {
-	os.Stderr.Write(stack())
+	os.Stderr.Write(Stack())
 }
 
 // Stack returns a formatted stack trace of the goroutine that calls it.
 // For each routine, it includes the source line information and PC value,
 // then attempts to discover, for Go functions, the calling function or
-// method and the text of the line containing the invocation.
-//
-// Deprecated: Use package runtime's Stack instead.
+// method.
 func Stack() []byte {
-	return stack()
-}
-
-// stack implements Stack, skipping 2 frames
-func stack() []byte {
-	buf := new(bytes.Buffer) // the returned data
-	// As we loop, we open files and read them. These variables record the currently
-	// loaded file.
-	var lines [][]byte
-	var lastFile string
-	for i := 2; ; i++ { // Caller we care about is the user, 2 frames up
-		pc, file, line, ok := runtime.Caller(i)
-		if !ok {
-			break
+	buf := make([]byte, 1024)
+	for {
+		n := runtime.Stack(buf, false)
+		if n < len(buf) {
+			return buf[:n]
 		}
-		// Print this much at least.  If we can't find the source, it won't show.
-		fmt.Fprintf(buf, "%s:%d (0x%x)\n", file, line, pc)
-		if file != lastFile {
-			data, err := ioutil.ReadFile(file)
-			if err != nil {
-				continue
-			}
-			lines = bytes.Split(data, []byte{'\n'})
-			lastFile = file
-		}
-		line-- // in stack trace, lines are 1-indexed but our array is 0-indexed
-		fmt.Fprintf(buf, "\t%s: %s\n", function(pc), source(lines, line))
+		buf = make([]byte, 2*len(buf))
 	}
-	return buf.Bytes()
-}
-
-// source returns a space-trimmed slice of the n'th line.
-func source(lines [][]byte, n int) []byte {
-	if n < 0 || n >= len(lines) {
-		return dunno
-	}
-	return bytes.Trim(lines[n], " \t")
-}
-
-// function returns, if possible, the name of the function containing the PC.
-func function(pc uintptr) []byte {
-	fn := runtime.FuncForPC(pc)
-	if fn == nil {
-		return dunno
-	}
-	name := []byte(fn.Name())
-	// The name includes the path name to the package, which is unnecessary
-	// since the file name is already included.  Plus, it has center dots.
-	// That is, we see
-	//	runtime/debug.*T·ptrmethod
-	// and want
-	//	*T.ptrmethod
-	// Since the package path might contains dots (e.g. code.google.com/...),
-	// we first remove the path prefix if there is one.
-	if lastslash := bytes.LastIndex(name, slash); lastslash >= 0 {
-		name = name[lastslash+1:]
-	}
-	if period := bytes.Index(name, dot); period >= 0 {
-		name = name[period+1:]
-	}
-	name = bytes.Replace(name, centerDot, dot, -1)
-	return name
 }
diff --git a/src/runtime/debug/stack_test.go b/src/runtime/debug/stack_test.go
index 28691ee..d2a4ea5 100644
--- a/src/runtime/debug/stack_test.go
+++ b/src/runtime/debug/stack_test.go
@@ -22,16 +22,19 @@
 	The traceback should look something like this, modulo line numbers and hex constants.
 	Don't worry much about the base levels, but check the ones in our own package.
 
-		/Users/r/go/src/runtime/debug/stack_test.go:15 (0x13878)
-			(*T).ptrmethod: return Stack()
-		/Users/r/go/src/runtime/debug/stack_test.go:18 (0x138dd)
-			T.method: return t.ptrmethod()
-		/Users/r/go/src/runtime/debug/stack_test.go:23 (0x13920)
-			TestStack: b := T(0).method()
-		/Users/r/go/src/testing/testing.go:132 (0x14a7a)
-			tRunner: test.F(t)
-		/Users/r/go/src/runtime/proc.c:145 (0xc970)
-			???: runtime·unlock(&runtime·sched);
+		goroutine 10 [running]:
+		runtime/debug.Stack(0x0, 0x0, 0x0)
+			/Users/r/go/src/runtime/debug/stack.go:28 +0x80
+		runtime/debug.(*T).ptrmethod(0xc82005ee70, 0x0, 0x0, 0x0)
+			/Users/r/go/src/runtime/debug/stack_test.go:15 +0x29
+		runtime/debug.T.method(0x0, 0x0, 0x0, 0x0)
+			/Users/r/go/src/runtime/debug/stack_test.go:18 +0x32
+		runtime/debug.TestStack(0xc8201ce000)
+			/Users/r/go/src/runtime/debug/stack_test.go:37 +0x38
+		testing.tRunner(0xc8201ce000, 0x664b58)
+			/Users/r/go/src/testing/testing.go:456 +0x98
+		created by testing.RunTests
+			/Users/r/go/src/testing/testing.go:561 +0x86d
 */
 func TestStack(t *testing.T) {
 	b := T(0).method()
@@ -41,17 +44,16 @@
 	}
 	n := 0
 	frame := func(line, code string) {
+		check(t, lines[n], code)
+		n++
 		check(t, lines[n], line)
 		n++
-		// The source might not be available while running the test.
-		if strings.HasPrefix(lines[n], "\t") {
-			check(t, lines[n], code)
-			n++
-		}
 	}
-	frame("src/runtime/debug/stack_test.go", "\t(*T).ptrmethod: return Stack()")
-	frame("src/runtime/debug/stack_test.go", "\tT.method: return t.ptrmethod()")
-	frame("src/runtime/debug/stack_test.go", "\tTestStack: b := T(0).method()")
+	n++
+	frame("src/runtime/debug/stack.go", "runtime/debug.Stack")
+	frame("src/runtime/debug/stack_test.go", "runtime/debug.(*T).ptrmethod")
+	frame("src/runtime/debug/stack_test.go", "runtime/debug.T.method")
+	frame("src/runtime/debug/stack_test.go", "runtime/debug.TestStack")
 	frame("src/testing/testing.go", "")
 }