diff --git a/src/go/internal/gcimporter/bimport.go b/src/go/internal/gcimporter/bimport.go
index 2a8b98b66f..ad28ef7735 100644
--- a/src/go/internal/gcimporter/bimport.go
+++ b/src/go/internal/gcimporter/bimport.go
@@ -13,6 +13,7 @@ import (
 	"sort"
 	"strconv"
 	"strings"
+	"sync"
 	"unicode"
 	"unicode/utf8"
 )
@@ -34,6 +35,8 @@ type importer struct {
 	posInfoFormat bool
 	prevFile      string
 	prevLine      int
+	fset          *token.FileSet
+	files         map[string]*token.File
 
 	// debugging support
 	debugFormat bool
@@ -44,7 +47,7 @@ type importer struct {
 // and returns the number of bytes consumed and a reference to the package.
 // If the export data version is not recognized or the format is otherwise
 // compromised, an error is returned.
-func BImportData(imports map[string]*types.Package, data []byte, path string) (_ int, _ *types.Package, err error) {
+func BImportData(fset *token.FileSet, imports map[string]*types.Package, data []byte, path string) (_ int, _ *types.Package, err error) {
 	// catch panics and return them as errors
 	defer func() {
 		if e := recover(); e != nil {
@@ -60,6 +63,8 @@ func BImportData(imports map[string]*types.Package, data []byte, path string) (_
 		path:    path,
 		version: -1,           // unknown version
 		strList: []string{""}, // empty string is mapped to 0
+		fset:    fset,
+		files:   make(map[string]*token.File),
 	}
 
 	// read version info
@@ -219,37 +224,37 @@ func (p *importer) declare(obj types.Object) {
 func (p *importer) obj(tag int) {
 	switch tag {
 	case constTag:
-		p.pos()
+		pos := p.pos()
 		pkg, name := p.qualifiedName()
 		typ := p.typ(nil)
 		val := p.value()
-		p.declare(types.NewConst(token.NoPos, pkg, name, typ, val))
+		p.declare(types.NewConst(pos, pkg, name, typ, val))
 
 	case typeTag:
 		_ = p.typ(nil)
 
 	case varTag:
-		p.pos()
+		pos := p.pos()
 		pkg, name := p.qualifiedName()
 		typ := p.typ(nil)
-		p.declare(types.NewVar(token.NoPos, pkg, name, typ))
+		p.declare(types.NewVar(pos, pkg, name, typ))
 
 	case funcTag:
-		p.pos()
+		pos := p.pos()
 		pkg, name := p.qualifiedName()
 		params, isddd := p.paramList()
 		result, _ := p.paramList()
 		sig := types.NewSignature(nil, params, result, isddd)
-		p.declare(types.NewFunc(token.NoPos, pkg, name, sig))
+		p.declare(types.NewFunc(pos, pkg, name, sig))
 
 	default:
 		errorf("unexpected object tag %d", tag)
 	}
 }
 
-func (p *importer) pos() {
+func (p *importer) pos() token.Pos {
 	if !p.posInfoFormat {
-		return
+		return token.NoPos
 	}
 
 	file := p.prevFile
@@ -265,9 +270,40 @@ func (p *importer) pos() {
 	}
 	p.prevLine = line
 
-	// TODO(gri) register new position
+	// Synthesize a token.Pos
+
+	// Since we don't know the set of needed file positions, we
+	// reserve maxlines positions per file.
+	const maxlines = 64 * 1024
+	f := p.files[file]
+	if f == nil {
+		f = p.fset.AddFile(file, -1, maxlines)
+		p.files[file] = f
+		// Allocate the fake linebreak indices on first use.
+		// TODO(adonovan): opt: save ~512KB using a more complex scheme?
+		fakeLinesOnce.Do(func() {
+			fakeLines = make([]int, maxlines)
+			for i := range fakeLines {
+				fakeLines[i] = i
+			}
+		})
+		f.SetLines(fakeLines)
+	}
+
+	if line > maxlines {
+		line = 1
+	}
+
+	// Treat the file as if it contained only newlines
+	// and column=1: use the line number as the offset.
+	return f.Pos(line - 1)
 }
 
+var (
+	fakeLines     []int
+	fakeLinesOnce sync.Once
+)
+
 func (p *importer) qualifiedName() (pkg *types.Package, name string) {
 	name = p.string()
 	pkg = p.pkg()
@@ -303,14 +339,14 @@ func (p *importer) typ(parent *types.Package) types.Type {
 	switch i {
 	case namedTag:
 		// read type object
-		p.pos()
+		pos := p.pos()
 		parent, name := p.qualifiedName()
 		scope := parent.Scope()
 		obj := scope.Lookup(name)
 
 		// if the object doesn't exist yet, create and insert it
 		if obj == nil {
-			obj = types.NewTypeName(token.NoPos, parent, name, nil)
+			obj = types.NewTypeName(pos, parent, name, nil)
 			scope.Insert(obj)
 		}
 
@@ -336,7 +372,7 @@ func (p *importer) typ(parent *types.Package) types.Type {
 		// read associated methods
 		for i := p.int(); i > 0; i-- {
 			// TODO(gri) replace this with something closer to fieldName
-			p.pos()
+			pos := p.pos()
 			name := p.string()
 			if !exported(name) {
 				p.pkg()
@@ -348,7 +384,7 @@ func (p *importer) typ(parent *types.Package) types.Type {
 			p.int() // go:nointerface pragma - discarded
 
 			sig := types.NewSignature(recv.At(0), params, result, isddd)
-			t0.AddMethod(types.NewFunc(token.NoPos, parent, name, sig))
+			t0.AddMethod(types.NewFunc(pos, parent, name, sig))
 		}
 
 		return t
@@ -483,7 +519,7 @@ func (p *importer) fieldList(parent *types.Package) (fields []*types.Var, tags [
 }
 
 func (p *importer) field(parent *types.Package) *types.Var {
-	p.pos()
+	pos := p.pos()
 	pkg, name := p.fieldName(parent)
 	typ := p.typ(parent)
 
@@ -502,7 +538,7 @@ func (p *importer) field(parent *types.Package) *types.Var {
 		anonymous = true
 	}
 
-	return types.NewField(token.NoPos, pkg, name, typ, anonymous)
+	return types.NewField(pos, pkg, name, typ, anonymous)
 }
 
 func (p *importer) methodList(parent *types.Package) (methods []*types.Func) {
@@ -516,12 +552,12 @@ func (p *importer) methodList(parent *types.Package) (methods []*types.Func) {
 }
 
 func (p *importer) method(parent *types.Package) *types.Func {
-	p.pos()
+	pos := p.pos()
 	pkg, name := p.fieldName(parent)
 	params, isddd := p.paramList()
 	result, _ := p.paramList()
 	sig := types.NewSignature(nil, params, result, isddd)
-	return types.NewFunc(token.NoPos, pkg, name, sig)
+	return types.NewFunc(pos, pkg, name, sig)
 }
 
 func (p *importer) fieldName(parent *types.Package) (*types.Package, string) {
@@ -613,6 +649,8 @@ func (p *importer) value() constant.Value {
 		return constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
 	case stringTag:
 		return constant.MakeString(p.string())
+	case unknownTag:
+		return constant.MakeUnknown()
 	default:
 		errorf("unexpected value tag %d", tag)
 		panic("unreachable")
diff --git a/src/go/internal/gcimporter/gcimporter.go b/src/go/internal/gcimporter/gcimporter.go
index 1e1102a451..f99f0f8bef 100644
--- a/src/go/internal/gcimporter/gcimporter.go
+++ b/src/go/internal/gcimporter/gcimporter.go
@@ -9,6 +9,7 @@ import (
 	"bufio"
 	"fmt"
 	"go/build"
+	"go/token"
 	"go/types"
 	"io/ioutil"
 	"os"
@@ -123,7 +124,10 @@ func Import(packages map[string]*types.Package, path, srcDir string) (pkg *types
 		var data []byte
 		data, err = ioutil.ReadAll(buf)
 		if err == nil {
-			_, pkg, err = BImportData(packages, data, id)
+			// TODO(gri): allow clients of go/importer to provide a FileSet.
+			// Or, define a new standard go/types/gcexportdata package.
+			fset := token.NewFileSet()
+			_, pkg, err = BImportData(fset, packages, data, id)
 			return
 		}
 	default: