diff --git a/go/gcimporter15/bexport.go b/go/gcimporter15/bexport.go
index 8eb048eb..36bcf035 100644
--- a/go/gcimporter15/bexport.go
+++ b/go/gcimporter15/bexport.go
@@ -32,9 +32,6 @@ const (
 )
 
 // BExportData returns binary export data for pkg.
-//
-// It is not safe to call this function on a package containing errors.
-// TODO(adonovan): add InvalidType to the protocol and lift this restriction.
 func BExportData(pkg *types.Package) []byte {
 	p := exporter{
 		pkgIndex: make(map[*types.Package]int),
@@ -209,9 +206,6 @@ func (p *exporter) typ(t types.Type) {
 	if t == nil {
 		log.Fatalf("nil type")
 	}
-	if t == types.Typ[types.Invalid] {
-		log.Fatal("BExportData invoked on package with errors")
-	}
 
 	// Possible optimization: Anonymous pointer types *T where
 	// T is a named type are common. We could canonicalize all
@@ -489,6 +483,10 @@ func (p *exporter) value(x constant.Value) {
 		p.tag(stringTag)
 		p.string(constant.StringVal(x))
 
+	case constant.Unknown:
+		// (Package contains type errors.)
+		p.tag(unknownTag)
+
 	default:
 		log.Fatalf("unexpected value %v (%T)", x, x)
 	}
@@ -700,4 +698,5 @@ var tagString = [...]string{
 	-fractionTag: "fraction",
 	-complexTag:  "complex",
 	-stringTag:   "string",
+	-unknownTag:  "unknown",
 }
diff --git a/go/gcimporter15/bexport_test.go b/go/gcimporter15/bexport_test.go
index fea4536f..941f7515 100644
--- a/go/gcimporter15/bexport_test.go
+++ b/go/gcimporter15/bexport_test.go
@@ -30,11 +30,25 @@ func TestBExportData_stdlib(t *testing.T) {
 	// Load, parse and type-check the program.
 	ctxt := build.Default // copy
 	ctxt.GOPATH = ""      // disable GOPATH
-	conf := loader.Config{Build: &ctxt}
+	conf := loader.Config{
+		Build:       &ctxt,
+		AllowErrors: true,
+	}
 	for _, path := range buildutil.AllPackages(conf.Build) {
 		conf.Import(path)
 	}
 
+	// Create a package containing type and value errors to ensure
+	// they are properly encoded/decoded.
+	f, err := conf.ParseFile("haserrors/haserrors.go", `package haserrors
+const UnknownValue = "" + 0
+type UnknownType undefined
+`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	conf.CreateFromFiles("haserrors", f)
+
 	prog, err := conf.Load()
 	if err != nil {
 		t.Fatalf("Load failed: %v", err)
@@ -49,7 +63,6 @@ func TestBExportData_stdlib(t *testing.T) {
 		if info.Files == nil {
 			continue // empty directory
 		}
-
 		exportdata := gcimporter.BExportData(pkg)
 
 		imports := make(map[string]*types.Package)
diff --git a/go/gcimporter15/bimport.go b/go/gcimporter15/bimport.go
index 0ec216e9..a39e3261 100644
--- a/go/gcimporter15/bimport.go
+++ b/go/gcimporter15/bimport.go
@@ -471,6 +471,9 @@ func (p *importer) value() constant.Value {
 		return constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
 	case stringTag:
 		return constant.MakeString(p.string())
+	case unknownTag:
+		// (Encoded package contains type errors.)
+		return constant.MakeUnknown()
 	default:
 		panic(fmt.Sprintf("unexpected value tag %d", tag))
 	}
@@ -644,6 +647,7 @@ const (
 	fractionTag // not used by gc
 	complexTag
 	stringTag
+	unknownTag // only appears in packages with errors
 )
 
 var predeclared = []types.Type{
@@ -685,7 +689,10 @@ var predeclared = []types.Type{
 	// package unsafe
 	types.Typ[types.UnsafePointer],
 
-	// any type, for builtin export data
+	// invalid type
+	types.Typ[types.Invalid], // only appears in packages with errors
+
 	// TODO(mdempsky): Provide an actual Type value to represent "any"?
+	// (Why exactly does gc emit the "any" type?)
 	types.Typ[types.Invalid],
 }