diff --git a/go/buildutil/allpackages.go b/go/buildutil/allpackages.go
index 0f909eeb..d28a5d0e 100644
--- a/go/buildutil/allpackages.go
+++ b/go/buildutil/allpackages.go
@@ -18,9 +18,10 @@ import (
 	"sync"
 )
 
-// AllPackages returns the import path of each Go package in any source
+// AllPackages returns the package path of each Go package in any source
 // directory of the specified build context (e.g. $GOROOT or an element
 // of $GOPATH).  Errors are ignored.  The results are sorted.
+// All package paths are canonical, and thus may contain "/vendor/".
 //
 // The result may include import paths for directories that contain no
 // *.go files, such as "archive" (in $GOROOT/src).
@@ -37,9 +38,10 @@ func AllPackages(ctxt *build.Context) []string {
 	return list
 }
 
-// ForEachPackage calls the found function with the import path of
+// ForEachPackage calls the found function with the package path of
 // each Go package it finds in any source directory of the specified
 // build context (e.g. $GOROOT or an element of $GOPATH).
+// All package paths are canonical, and thus may contain "/vendor/".
 //
 // If the package directory exists but could not be read, the second
 // argument to the found function provides the error.
diff --git a/go/buildutil/buildutil_go15.go b/go/buildutil/buildutil_go15.go
new file mode 100644
index 00000000..d1640b14
--- /dev/null
+++ b/go/buildutil/buildutil_go15.go
@@ -0,0 +1,14 @@
+// Copyright 2015 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.
+
+// +build !go1.6
+
+package buildutil
+
+import "go/build"
+
+// AllowVendor is a synonym for zero.
+// It allows applications to refer to the go/build.AllowVendor
+// feature whether or not it is supported.
+const AllowVendor build.ImportMode = 0
diff --git a/go/buildutil/buildutil_go16.go b/go/buildutil/buildutil_go16.go
new file mode 100644
index 00000000..c5703d72
--- /dev/null
+++ b/go/buildutil/buildutil_go16.go
@@ -0,0 +1,14 @@
+// Copyright 2015 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.
+
+// +build go1.6
+
+package buildutil
+
+import "go/build"
+
+// AllowVendor is a synonym for go/build.AllowVendor.
+// It allows applications to refer to the AllowVendor
+// feature whether or not it is supported.
+const AllowVendor build.ImportMode = build.AllowVendor
diff --git a/go/buildutil/util.go b/go/buildutil/util.go
index 0e093fc0..c4bdd29f 100644
--- a/go/buildutil/util.go
+++ b/go/buildutil/util.go
@@ -90,6 +90,15 @@ func dirHasPrefix(dir, prefix string) bool {
 	return len(dir) >= len(prefix) && strings.EqualFold(dir[:len(prefix)], prefix)
 }
 
+// StripVendor removes the "vendor" segment and all preceding ones
+// from a slash-segmented path.  (See go/build.AllowVendor.)
+func StripVendor(path string) string {
+	if i := strings.LastIndex(path, "/vendor/"); i >= 0 {
+		return path[i+len("/vendor/"):]
+	}
+	return strings.TrimPrefix(path, "vendor/")
+}
+
 // -- Effective methods of file system interface -------------------------
 
 // (go/build.Context defines these as methods, but does not export them.)
diff --git a/go/buildutil/util_test.go b/go/buildutil/util_test.go
index 10dae177..b6350229 100644
--- a/go/buildutil/util_test.go
+++ b/go/buildutil/util_test.go
@@ -29,6 +29,8 @@ func TestContainingPackage(t *testing.T) {
 		{goroot + "/src/encoding/missing/foo.go", "(not found)"},
 		{gopath + "/src/golang.org/x/tools/go/buildutil/util_test.go",
 			"golang.org/x/tools/go/buildutil"},
+		{gopath + "/src/vendor/golang.org/x/net/http2/hpack/hpack.go",
+			"vendor/golang.org/x/net/http2/hpack"},
 	} {
 		file, want := test[0], test[1]
 		bp, err := buildutil.ContainingPackage(&build.Default, ".", file)
@@ -43,3 +45,22 @@ func TestContainingPackage(t *testing.T) {
 
 	// TODO(adonovan): test on virtualized GOPATH too.
 }
+
+func TestStripVendor(t *testing.T) {
+	for _, test := range []struct {
+		path, want string
+	}{
+		{"", ""},
+		{"a", "a"},
+		{"a/b", "a/b"},
+		{"a/vendor/b", "b"},
+		{"a/b/vendor/c/d", "c/d"},
+		{"vendor/a/b", "a/b"},
+		{"a/vendor", "a/vendor"},
+	} {
+		if got := buildutil.StripVendor(test.path); got != test.want {
+			t.Errorf("StripVendor(%q) = %q, want %q",
+				test.path, got, test.want)
+		}
+	}
+}