diff --git a/gen.go b/gen.go
index 8cb50c7..ed2bf24 100644
--- a/gen.go
+++ b/gen.go
@@ -3,15 +3,24 @@ package typegen
 import (
 	"fmt"
 	"io"
+	"math/big"
 	"reflect"
 	"strings"
 	"text/template"
+
+	"github.com/ipfs/go-cid"
 )
 
 const MaxLength = 8192
 
 const ByteArrayMaxLen = 2 << 20
 
+var (
+	cidType      = reflect.TypeOf(cid.Cid{})
+	bigIntType   = reflect.TypeOf(big.Int{})
+	deferredType = reflect.TypeOf(Deferred{})
+)
+
 func doTemplate(w io.Writer, info interface{}, templ string) error {
 	t := template.Must(template.New("").
 		Funcs(template.FuncMap{
@@ -28,10 +37,19 @@ func doTemplate(w io.Writer, info interface{}, templ string) error {
 	return t.Execute(w, info)
 }
 
-func PrintHeaderAndUtilityMethods(w io.Writer, pkg string) error {
+func PrintHeaderAndUtilityMethods(w io.Writer, pkg string, typeInfos []*GenTypeInfo) error {
+	var imports []Import
+	for _, gti := range typeInfos {
+		imports = append(imports, gti.Imports()...)
+	}
+
+	imports = append(imports, defaultImports...)
+	imports = dedupImports(imports)
+
 	data := struct {
 		Package string
-	}{pkg}
+		Imports []Import
+	}{pkg, imports}
 	return doTemplate(w, data, `// Code generated by github.com/whyrusleeping/cbor-gen. DO NOT EDIT.
 
 package {{ .Package }}
@@ -39,8 +57,9 @@ package {{ .Package }}
 import (
 	"fmt"
 	"io"
-	cbg "github.com/whyrusleeping/cbor-gen"
-	xerrors "golang.org/x/xerrors"
+
+{{ range .Imports }}{{ .Name }} "{{ .PkgPath }}"
+{{ end }}
 )
 
 
@@ -69,13 +88,14 @@ func typeName(pkg string, t reflect.Type) string {
 	case reflect.Map:
 		return "map[" + typeName(pkg, t.Key()) + "]" + typeName(pkg, t.Elem())
 	default:
-		name := t.String()
-		if t.PkgPath() == "github.com/whyrusleeping/cbor-gen" {
-			name = "cbg." + strings.TrimPrefix(name, "typegen.")
-		} else {
-			name = strings.TrimPrefix(name, pkg+".")
+		pkgPath := t.PkgPath()
+		if pkgPath == "" {
+			// It's a built-in.
+			return t.String()
+		} else if pkgPath == pkg {
+			return t.Name()
 		}
-		return name
+		return fmt.Sprintf("%s.%s", resolvePkgName(pkgPath, t.String()), t.Name())
 	}
 }
 
@@ -100,6 +120,25 @@ type GenTypeInfo struct {
 	Fields []Field
 }
 
+func (gti *GenTypeInfo) Imports() []Import {
+	var imports []Import
+	for _, f := range gti.Fields {
+		switch f.Type.Kind() {
+		case reflect.Struct:
+			if !f.Pointer && f.Type != bigIntType {
+				continue
+			}
+			if f.Type == cidType {
+				continue
+			}
+		case reflect.Bool:
+			continue
+		}
+		imports = append(imports, ImportsForType(f.Pkg, f.Type)...)
+	}
+	return imports
+}
+
 func (gti *GenTypeInfo) NeedsScratch() bool {
 	for _, f := range gti.Fields {
 		switch f.Type.Kind() {
@@ -113,11 +152,7 @@ func (gti *GenTypeInfo) NeedsScratch() bool {
 			return true
 
 		case reflect.Struct:
-			fname := f.Type.PkgPath() + "." + f.Type.Name()
-			switch fname {
-			case "math/big.Int":
-				return true
-			case "github.com/ipfs/go-cid.Cid":
+			if f.Type == bigIntType || f.Type == cidType {
 				return true
 			}
 			// nope
@@ -132,9 +167,11 @@ func nameIsExported(name string) bool {
 	return strings.ToUpper(name[0:1]) == name[0:1]
 }
 
-func ParseTypeInfo(pkg string, i interface{}) (*GenTypeInfo, error) {
+func ParseTypeInfo(i interface{}) (*GenTypeInfo, error) {
 	t := reflect.TypeOf(i)
 
+	pkg := t.PkgPath()
+
 	out := GenTypeInfo{
 		Name: t.Name(),
 	}
@@ -208,9 +245,8 @@ func emitCborMarshalStringField(w io.Writer, f Field) error {
 `)
 }
 func emitCborMarshalStructField(w io.Writer, f Field) error {
-	fname := f.Type.PkgPath() + "." + f.Type.Name()
-	switch fname {
-	case "math/big.Int":
+	switch f.Type {
+	case bigIntType:
 		return doTemplate(w, f, `
 	{
 		if err := cbg.CborWriteHeader(w, cbg.MajTag, 2); err != nil {
@@ -230,7 +266,7 @@ func emitCborMarshalStructField(w io.Writer, f Field) error {
 	}
 `)
 
-	case "github.com/ipfs/go-cid.Cid":
+	case cidType:
 		return doTemplate(w, f, `
 {{ if .Pointer }}
 	if {{ .Name }} == nil {
@@ -403,9 +439,8 @@ func emitCborMarshalSliceField(w io.Writer, f Field) error {
 	default:
 		return fmt.Errorf("do not yet support slices of %s yet", e.Kind())
 	case reflect.Struct:
-		fname := e.PkgPath() + "." + e.Name()
-		switch fname {
-		case "github.com/ipfs/go-cid.Cid":
+		switch e {
+		case cidType:
 			err := doTemplate(w, f, `
 		if err := cbg.WriteCidBuf(scratch, w, v); err != nil {
 			return xerrors.Errorf("failed writing cid field {{ .Name }}: %w", err)
@@ -548,10 +583,8 @@ func emitCborUnmarshalStringField(w io.Writer, f Field) error {
 }
 
 func emitCborUnmarshalStructField(w io.Writer, f Field) error {
-	fname := f.Type.PkgPath() + "." + f.Type.Name()
-
-	switch fname {
-	case "math/big.Int":
+	switch f.Type {
+	case bigIntType:
 		return doTemplate(w, f, `
 	maj, extra, err = {{ ReadHeader "br" }}
 	if err != nil {
@@ -585,7 +618,7 @@ func emitCborUnmarshalStructField(w io.Writer, f Field) error {
 		{{ .Name }} = big.NewInt(0)
 	}
 `)
-	case "github.com/ipfs/go-cid.Cid":
+	case cidType:
 		return doTemplate(w, f, `
 	{
 {{ if .Pointer }}
@@ -610,7 +643,7 @@ func emitCborUnmarshalStructField(w io.Writer, f Field) error {
 {{ end }}
 	}
 `)
-	case "github.com/whyrusleeping/cbor-gen.Deferred":
+	case deferredType:
 		return doTemplate(w, f, `
 	{
 {{ if .Pointer }}
@@ -1059,12 +1092,7 @@ func (t *{{ .Name}}) UnmarshalCBOR(r io.Reader) error {
 }
 
 // Generates 'tuple representation' cbor encoders for the given type
-func GenTupleEncodersForType(inpkg string, i interface{}, w io.Writer) error {
-	gti, err := ParseTypeInfo(inpkg, i)
-	if err != nil {
-		return err
-	}
-
+func GenTupleEncodersForType(gti *GenTypeInfo, w io.Writer) error {
 	if err := emitCborMarshalStructTuple(w, gti); err != nil {
 		return err
 	}
@@ -1251,12 +1279,7 @@ func (t *{{ .Name}}) UnmarshalCBOR(r io.Reader) error {
 }
 
 // Generates 'tuple representation' cbor encoders for the given type
-func GenMapEncodersForType(inpkg string, i interface{}, w io.Writer) error {
-	gti, err := ParseTypeInfo(inpkg, i)
-	if err != nil {
-		return err
-	}
-
+func GenMapEncodersForType(gti *GenTypeInfo, w io.Writer) error {
 	if err := emitCborMarshalStructMap(w, gti); err != nil {
 		return err
 	}
diff --git a/package.go b/package.go
new file mode 100644
index 0000000..1943e09
--- /dev/null
+++ b/package.go
@@ -0,0 +1,99 @@
+package typegen
+
+import (
+	"fmt"
+	"reflect"
+	"sort"
+	"strings"
+	"sync"
+)
+
+var (
+	knownPackageNamesMu sync.Mutex
+	pkgNameToPkgPath    = make(map[string]string)
+	pkgPathToPkgName    = make(map[string]string)
+
+	defaultImports = []Import{
+		{Name: "cbg", PkgPath: "github.com/whyrusleeping/cbor-gen"},
+		{Name: "xerrors", PkgPath: "golang.org/x/xerrors"},
+	}
+)
+
+func init() {
+	for _, imp := range defaultImports {
+		if was, conflict := pkgNameToPkgPath[imp.Name]; conflict {
+			panic(fmt.Sprintf("reused pkg name %s for %s and %s", imp.Name, imp.PkgPath, was))
+		}
+		if _, conflict := pkgPathToPkgName[imp.Name]; conflict {
+			panic(fmt.Sprintf("duplicate default import %s", imp.PkgPath))
+		}
+		pkgNameToPkgPath[imp.Name] = imp.PkgPath
+		pkgPathToPkgName[imp.PkgPath] = imp.Name
+	}
+}
+
+func resolvePkgName(path, typeName string) string {
+	parts := strings.Split(typeName, ".")
+	if len(parts) != 2 {
+		panic(fmt.Sprintf("expected type to have a package name: %s", typeName))
+	}
+	defaultName := parts[0]
+
+	knownPackageNamesMu.Lock()
+	defer knownPackageNamesMu.Unlock()
+
+	// Check for a known name and use it.
+	if name, ok := pkgPathToPkgName[path]; ok {
+		return name
+	}
+
+	// Allocate a name.
+	for i := 0; ; i++ {
+		tryName := defaultName
+		if i > 0 {
+			tryName = fmt.Sprintf("%s%d", defaultName, i)
+		}
+		if _, taken := pkgNameToPkgPath[tryName]; !taken {
+			pkgNameToPkgPath[tryName] = path
+			pkgPathToPkgName[path] = tryName
+			return tryName
+		}
+	}
+
+}
+
+type Import struct {
+	Name, PkgPath string
+}
+
+func ImportsForType(currPkg string, t reflect.Type) []Import {
+	switch t.Kind() {
+	case reflect.Array, reflect.Slice, reflect.Ptr:
+		return ImportsForType(currPkg, t.Elem())
+	case reflect.Map:
+		return dedupImports(append(ImportsForType(currPkg, t.Key()), ImportsForType(currPkg, t.Elem())...))
+	default:
+		path := t.PkgPath()
+		if path == "" || path == currPkg {
+			// built-in or in current package.
+			return nil
+		}
+
+		return []Import{{PkgPath: path, Name: resolvePkgName(path, t.String())}}
+	}
+}
+
+func dedupImports(imps []Import) []Import {
+	impSet := make(map[string]string, len(imps))
+	for _, imp := range imps {
+		impSet[imp.PkgPath] = imp.Name
+	}
+	deduped := make([]Import, 0, len(imps))
+	for pkg, name := range impSet {
+		deduped = append(deduped, Import{Name: name, PkgPath: pkg})
+	}
+	sort.Slice(deduped, func(i, j int) bool {
+		return deduped[i].PkgPath < deduped[j].PkgPath
+	})
+	return deduped
+}
diff --git a/writefile.go b/writefile.go
index 18de6e6..6c9a63b 100644
--- a/writefile.go
+++ b/writefile.go
@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"go/format"
 	"os"
-	"os/exec"
 
 	"golang.org/x/xerrors"
 )
@@ -12,12 +11,21 @@ import (
 func WriteTupleEncodersToFile(fname, pkg string, types ...interface{}) error {
 	buf := new(bytes.Buffer)
 
-	if err := PrintHeaderAndUtilityMethods(buf, pkg); err != nil {
+	typeInfos := make([]*GenTypeInfo, len(types))
+	for i, t := range types {
+		gti, err := ParseTypeInfo(t)
+		if err != nil {
+			return xerrors.Errorf("failed to parse type info: %w", err)
+		}
+		typeInfos[i] = gti
+	}
+
+	if err := PrintHeaderAndUtilityMethods(buf, pkg, typeInfos); err != nil {
 		return xerrors.Errorf("failed to write header: %w", err)
 	}
 
-	for _, t := range types {
-		if err := GenTupleEncodersForType(pkg, t, buf); err != nil {
+	for _, t := range typeInfos {
+		if err := GenTupleEncodersForType(t, buf); err != nil {
 			return xerrors.Errorf("failed to generate encoders: %w", err)
 		}
 	}
@@ -39,22 +47,27 @@ func WriteTupleEncodersToFile(fname, pkg string, types ...interface{}) error {
 	}
 	_ = fi.Close()
 
-	if err := exec.Command("goimports", "-w", fname).Run(); err != nil {
-		return err
-	}
-
 	return nil
 }
 
 func WriteMapEncodersToFile(fname, pkg string, types ...interface{}) error {
 	buf := new(bytes.Buffer)
 
-	if err := PrintHeaderAndUtilityMethods(buf, pkg); err != nil {
+	typeInfos := make([]*GenTypeInfo, len(types))
+	for i, t := range types {
+		gti, err := ParseTypeInfo(t)
+		if err != nil {
+			return xerrors.Errorf("failed to parse type info: %w", err)
+		}
+		typeInfos[i] = gti
+	}
+
+	if err := PrintHeaderAndUtilityMethods(buf, pkg, typeInfos); err != nil {
 		return xerrors.Errorf("failed to write header: %w", err)
 	}
 
-	for _, t := range types {
-		if err := GenMapEncodersForType(pkg, t, buf); err != nil {
+	for _, t := range typeInfos {
+		if err := GenMapEncodersForType(t, buf); err != nil {
 			return xerrors.Errorf("failed to generate encoders: %w", err)
 		}
 	}
@@ -76,9 +89,5 @@ func WriteMapEncodersToFile(fname, pkg string, types ...interface{}) error {
 	}
 	_ = fi.Close()
 
-	if err := exec.Command("goimports", "-w", fname).Run(); err != nil {
-		return err
-	}
-
 	return nil
 }