diff --git a/Makefile b/Makefile
index 000314b..063c2a2 100644
--- a/Makefile
+++ b/Makefile
@@ -17,4 +17,22 @@ GOFILES=\
 	prf.go\
 	tls.go\
 
+ifeq ($(CGO_ENABLED),1)
+CGOFILES_darwin=\
+	root_darwin.go
+else
+GOFILES_darwin+=root_stub.go
+endif
+
+GOFILES_freebsd+=root_unix.go
+GOFILES_linux+=root_unix.go
+GOFILES_openbsd+=root_unix.go
+GOFILES_plan9+=root_stub.go
+GOFILES_windows+=root_stub.go
+
+GOFILES+=$(GOFILES_$(GOOS))
+ifneq ($(CGOFILES_$(GOOS)),)
+CGOFILES+=$(CGOFILES_$(GOOS))
+endif
+
 include ../../../Make.pkg
diff --git a/common.go b/common.go
index 8b4dafb..ea52085 100644
--- a/common.go
+++ b/common.go
@@ -9,7 +9,6 @@ import (
 	"crypto/rsa"
 	"crypto/x509"
 	"io"
-	"io/ioutil"
 	"strings"
 	"sync"
 	"time"
@@ -155,6 +154,14 @@ type Config struct {
 	// anything more than self-signed.
 	AuthenticateClient bool
 
+	// InsecureSkipVerify controls whether a client verifies the
+	// server's certificate chain and host name.
+	// If InsecureSkipVerify is true, TLS accepts any certificate
+	// presented by the server and any host name in that certificate.
+	// In this mode, TLS is susceptible to man-in-the-middle attacks.
+	// This should be used only for testing.
+	InsecureSkipVerify bool
+
 	// CipherSuites is a list of supported cipher suites. If CipherSuites
 	// is nil, TLS uses a list of suites supported by the implementation.
 	CipherSuites []uint16
@@ -284,15 +291,6 @@ func defaultConfig() *Config {
 	return &emptyConfig
 }
 
-// Possible certificate files; stop after finding one.
-// On OS X we should really be using the Directory Services keychain
-// but that requires a lot of Mach goo to get at.  Instead we use
-// the same root set that curl uses.
-var certFiles = []string{
-	"/etc/ssl/certs/ca-certificates.crt", // Linux etc
-	"/usr/share/curl/curl-ca-bundle.crt", // OS X
-}
-
 var once sync.Once
 
 func defaultRoots() *x509.CertPool {
@@ -310,21 +308,10 @@ func initDefaults() {
 	initDefaultCipherSuites()
 }
 
-var varDefaultRoots *x509.CertPool
-
-func initDefaultRoots() {
-	roots := x509.NewCertPool()
-	for _, file := range certFiles {
-		data, err := ioutil.ReadFile(file)
-		if err == nil {
-			roots.AppendCertsFromPEM(data)
-			break
-		}
-	}
-	varDefaultRoots = roots
-}
-
-var varDefaultCipherSuites []uint16
+var (
+	varDefaultRoots        *x509.CertPool
+	varDefaultCipherSuites []uint16
+)
 
 func initDefaultCipherSuites() {
 	varDefaultCipherSuites = make([]uint16, len(cipherSuites))
diff --git a/handshake_client.go b/handshake_client.go
index 0badc39..575a121 100644
--- a/handshake_client.go
+++ b/handshake_client.go
@@ -97,11 +97,9 @@ func (c *Conn) clientHandshake() os.Error {
 		certs[i] = cert
 	}
 
-	// If we don't have a root CA set configured then anything is accepted.
-	// TODO(rsc): Find certificates for OS X 10.6.
-	if c.config.RootCAs != nil {
+	if !c.config.InsecureSkipVerify {
 		opts := x509.VerifyOptions{
-			Roots:         c.config.RootCAs,
+			Roots:         c.config.rootCAs(),
 			CurrentTime:   c.config.time(),
 			DNSName:       c.config.ServerName,
 			Intermediates: x509.NewCertPool(),
diff --git a/handshake_server_test.go b/handshake_server_test.go
index 9873eb3..1939f3d 100644
--- a/handshake_server_test.go
+++ b/handshake_server_test.go
@@ -38,6 +38,7 @@ func init() {
 	testConfig.Certificates[0].Certificate = [][]byte{testCertificate}
 	testConfig.Certificates[0].PrivateKey = testPrivateKey
 	testConfig.CipherSuites = []uint16{TLS_RSA_WITH_RC4_128_SHA}
+	testConfig.InsecureSkipVerify = true
 }
 
 func testClientHelloFailure(t *testing.T, m handshakeMessage, expected os.Error) {
diff --git a/root_darwin.go b/root_darwin.go
new file mode 100644
index 0000000..1512241
--- /dev/null
+++ b/root_darwin.go
@@ -0,0 +1,95 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tls
+
+/*
+// Note: We disable -Werror here because the code in this file uses a deprecated API to stay
+// compatible with both Mac OS X 10.6 and 10.7. Using a deprecated function on Darwin generates
+// a warning.
+#cgo CFLAGS: -Wno-error
+#cgo LDFLAGS: -framework CoreFoundation -framework Security
+#include <CoreFoundation/CoreFoundation.h>
+#include <Security/Security.h>
+
+// FetchPEMRoots fetches the system's list of trusted X.509 root certificates.
+//
+// On success it returns 0 and fills pemRoots with a CFDataRef that contains the extracted root
+// certificates of the system. On failure, the function returns -1.
+//
+// Note: The CFDataRef returned in pemRoots must be released (using CFRelease) after
+// we've consumed its content.
+int FetchPEMRoots(CFDataRef *pemRoots) {
+	if (pemRoots == NULL) {
+		return -1;
+	}
+
+	CFArrayRef certs = NULL;
+	OSStatus err = SecTrustCopyAnchorCertificates(&certs);
+	if (err != noErr) {
+		return -1;
+	}
+
+	CFMutableDataRef combinedData = CFDataCreateMutable(kCFAllocatorDefault, 0);
+	int i, ncerts = CFArrayGetCount(certs);
+	for (i = 0; i < ncerts; i++) {
+		CFDataRef data = NULL;
+		SecCertificateRef cert = (SecCertificateRef)CFArrayGetValueAtIndex(certs, i);
+		if (cert == NULL) {
+			continue;
+		}
+
+		// SecKeychainImportExport is deprecated in >= OS X 10.7, and has been replaced by
+		// SecItemExport.  If we're built on a host with a Lion SDK, this code gets conditionally
+		// included in the output, also for binaries meant for 10.6.
+		//
+		// To make sure that we run on both Mac OS X 10.6 and 10.7 we use weak linking
+		// and check whether SecItemExport is available before we attempt to call it. On
+		// 10.6, this won't be the case, and we'll fall back to calling SecKeychainItemExport.
+#if __MAC_OS_X_VERSION_MAX_ALLOWED >= 1070
+		if (SecItemExport) {
+			err = SecItemExport(cert, kSecFormatX509Cert, kSecItemPemArmour, NULL, &data);
+			if (err != noErr) {
+				continue;
+			}
+		} else
+#endif
+		if (data == NULL) {
+			err = SecKeychainItemExport(cert, kSecFormatX509Cert, kSecItemPemArmour, NULL, &data);
+			if (err != noErr) {
+				continue;
+			}
+		}
+
+		if (data != NULL) {
+			CFDataAppendBytes(combinedData, CFDataGetBytePtr(data), CFDataGetLength(data));
+			CFRelease(data);
+		}
+	}
+
+	CFRelease(certs);
+
+	*pemRoots = combinedData;
+	return 0;
+}
+*/
+import "C"
+import (
+	"crypto/x509"
+	"unsafe"
+)
+
+func initDefaultRoots() {
+	roots := x509.NewCertPool()
+
+	var data C.CFDataRef = nil
+	err := C.FetchPEMRoots(&data)
+	if err != -1 {
+		defer C.CFRelease(C.CFTypeRef(data))
+		buf := C.GoBytes(unsafe.Pointer(C.CFDataGetBytePtr(data)), C.int(C.CFDataGetLength(data)))
+		roots.AppendCertsFromPEM(buf)
+	}
+
+	varDefaultRoots = roots
+}
diff --git a/root_stub.go b/root_stub.go
new file mode 100644
index 0000000..1903eed
--- /dev/null
+++ b/root_stub.go
@@ -0,0 +1,8 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tls
+
+func initDefaultRoots() {
+}
diff --git a/root_test.go b/root_test.go
new file mode 100644
index 0000000..95a89d8
--- /dev/null
+++ b/root_test.go
@@ -0,0 +1,36 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tls
+
+import (
+	"testing"
+)
+
+var tlsServers = []string{
+	"google.com:443",
+	"github.com:443",
+	"twitter.com:443",
+}
+
+func TestOSCertBundles(t *testing.T) {
+	defaultRoots()
+
+	if testing.Short() {
+		t.Logf("skipping certificate tests in short mode")
+		return
+	}
+
+	for _, addr := range tlsServers {
+		conn, err := Dial("tcp", addr, nil)
+		if err != nil {
+			t.Errorf("unable to verify %v: %v", addr, err)
+			continue
+		}
+		err = conn.Close()
+		if err != nil {
+			t.Error(err)
+		}
+	}
+}
diff --git a/root_unix.go b/root_unix.go
new file mode 100644
index 0000000..57af92a
--- /dev/null
+++ b/root_unix.go
@@ -0,0 +1,27 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tls
+
+import (
+	"crypto/x509"
+	"io/ioutil"
+)
+
+// Possible certificate files; stop after finding one.
+var certFiles = []string{
+	"/etc/ssl/certs/ca-certificates.crt", // Linux etc
+}
+
+func initDefaultRoots() {
+	roots := x509.NewCertPool()
+	for _, file := range certFiles {
+		data, err := ioutil.ReadFile(file)
+		if err == nil {
+			roots.AppendCertsFromPEM(data)
+			break
+		}
+	}
+	varDefaultRoots = roots
+}