diff --git a/internal/tests/mapconv/input.go b/internal/tests/mapconv/input.go
index 3542e46..990121f 100644
--- a/internal/tests/mapconv/input.go
+++ b/internal/tests/mapconv/input.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by the MIT license,
 // which can be found in the LICENSE file.
 
-//go:generate gencodec -type X -field-override Xo -out output.go
+//go:generate gencodec -type X -field-override Xo -formats json,yaml -out output.go
 
 package mapconv
 
diff --git a/internal/tests/nameclash/input.go b/internal/tests/nameclash/input.go
index 9c874d4..4e997d6 100644
--- a/internal/tests/nameclash/input.go
+++ b/internal/tests/nameclash/input.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by the MIT license,
 // which can be found in the LICENSE file.
 
-//go:generate gencodec -type Y -field-override Yo -out output.go
+//go:generate gencodec -type Y -field-override Yo -formats json,yaml -out output.go
 
 package nameclash
 
diff --git a/internal/tests/sliceconv/input.go b/internal/tests/sliceconv/input.go
index ad6ba8a..7112339 100644
--- a/internal/tests/sliceconv/input.go
+++ b/internal/tests/sliceconv/input.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by the MIT license,
 // which can be found in the LICENSE file.
 
-//go:generate gencodec -type X -field-override Xo -out output.go
+//go:generate gencodec -type X -field-override Xo -formats json,yaml -out output.go
 
 package sliceconv
 
diff --git a/main.go b/main.go
index 1e48609..f8fda42 100644
--- a/main.go
+++ b/main.go
@@ -121,13 +121,18 @@ import (
 func main() {
 	var (
 		pkgdir    = flag.String("dir", ".", "input package")
-		output    = flag.String("out", "-", "output file")
-		typename  = flag.String("type", "", "type to generate")
+		output    = flag.String("out", "-", "output file (default is stdout)")
+		typename  = flag.String("type", "", "type to generate methods for")
 		overrides = flag.String("field-override", "", "type to take field type replacements from")
+		formats   = flag.String("formats", "json", `marshaling formats (e.g. "json,yaml")`)
 	)
 	flag.Parse()
 
-	cfg := Config{Dir: *pkgdir, Type: *typename, FieldOverride: *overrides}
+	formatList := strings.Split(*formats, ",")
+	for i := range formatList {
+		formatList[i] = strings.TrimSpace(formatList[i])
+	}
+	cfg := Config{Dir: *pkgdir, Type: *typename, FieldOverride: *overrides, Formats: formatList}
 	code, err := cfg.process()
 	if err != nil {
 		fatal(err)
@@ -144,10 +149,13 @@ func fatal(args ...interface{}) {
 	os.Exit(1)
 }
 
+var AllFormats = []string{"json", "yaml"}
+
 type Config struct {
-	Dir           string // input package directory
-	Type          string // type to generate methods for
-	FieldOverride string // name of struct type for field overrides
+	Dir           string   // input package directory
+	Type          string   // type to generate methods for
+	FieldOverride string   // name of struct type for field overrides
+	Formats       []string // defaults to just "json", supported: "json", "yaml"
 	Importer      types.Importer
 	FileSet       *token.FileSet
 }
@@ -159,6 +167,9 @@ func (cfg *Config) process() (code []byte, err error) {
 	if cfg.Importer == nil {
 		cfg.Importer = importer.Default()
 	}
+	if cfg.Formats == nil {
+		cfg.Formats = []string{"json"}
+	}
 	pkg, err := loadPackage(cfg)
 	if err != nil {
 		return nil, err
@@ -183,7 +194,10 @@ func (cfg *Config) process() (code []byte, err error) {
 
 	// Generate and format the output. Formatting uses goimports because it
 	// removes unused imports.
-	code = genPackage(mtyp)
+	code, err = generate(mtyp, cfg)
+	if err != nil {
+		return nil, err
+	}
 	opt := &imports.Options{Comments: true, TabIndent: true, TabWidth: 8}
 	code, err = imports.Process("", code, opt)
 	if err != nil {
@@ -211,21 +225,29 @@ func loadPackage(cfg *Config) (*types.Package, error) {
 	return prog.Package(pkg.ImportPath).Pkg, nil
 }
 
-func genPackage(mtyp *marshalerType) []byte {
+func generate(mtyp *marshalerType, cfg *Config) ([]byte, error) {
 	w := new(bytes.Buffer)
 	fmt.Fprintln(w, "// generated by gencodec, do not edit.\n")
 	fmt.Fprintln(w, "package", mtyp.orig.Obj().Pkg().Name())
 	fmt.Fprintln(w)
 	mtyp.scope.writeImportDecl(w)
 	fmt.Fprintln(w)
-	writeFunction(w, mtyp.fs, genMarshalJSON(mtyp))
-	fmt.Fprintln(w)
-	writeFunction(w, mtyp.fs, genUnmarshalJSON(mtyp))
-	fmt.Fprintln(w)
-	writeFunction(w, mtyp.fs, genMarshalYAML(mtyp))
-	fmt.Fprintln(w)
-	writeFunction(w, mtyp.fs, genUnmarshalYAML(mtyp))
-	return w.Bytes()
+	for _, format := range cfg.Formats {
+		switch format {
+		case "json":
+			writeFunction(w, mtyp.fs, genMarshalJSON(mtyp))
+			fmt.Fprintln(w)
+			writeFunction(w, mtyp.fs, genUnmarshalJSON(mtyp))
+		case "yaml":
+			writeFunction(w, mtyp.fs, genMarshalYAML(mtyp))
+			fmt.Fprintln(w)
+			writeFunction(w, mtyp.fs, genUnmarshalYAML(mtyp))
+		default:
+			return nil, fmt.Errorf("unknown format: %q", format)
+		}
+		fmt.Fprintln(w)
+	}
+	return w.Bytes(), nil
 }
 
 // marshalerType represents the intermediate struct type used during marshaling.
diff --git a/main_test.go b/main_test.go
index 597460a..f2afa62 100644
--- a/main_test.go
+++ b/main_test.go
@@ -18,15 +18,15 @@ import (
 //    go generate ./internal/...
 
 func TestMapConv(t *testing.T) {
-	runGoldenTest(t, Config{Dir: "mapconv", Type: "X", FieldOverride: "Xo"})
+	runGoldenTest(t, Config{Dir: "mapconv", Type: "X", FieldOverride: "Xo", Formats: AllFormats})
 }
 
 func TestSliceConv(t *testing.T) {
-	runGoldenTest(t, Config{Dir: "sliceconv", Type: "X", FieldOverride: "Xo"})
+	runGoldenTest(t, Config{Dir: "sliceconv", Type: "X", FieldOverride: "Xo", Formats: AllFormats})
 }
 
 func TestNameClash(t *testing.T) {
-	runGoldenTest(t, Config{Dir: "nameclash", Type: "Y", FieldOverride: "Yo"})
+	runGoldenTest(t, Config{Dir: "nameclash", Type: "Y", FieldOverride: "Yo", Formats: AllFormats})
 }
 
 func runGoldenTest(t *testing.T, cfg Config) {