diff --git a/printer/print.go b/printer/print.go
index b90d03d9..44c31786 100644
--- a/printer/print.go
+++ b/printer/print.go
@@ -1,7 +1,7 @@
 package printer
 
 import (
-	"bufio"
+	"bytes"
 	"fmt"
 	"github.com/tinylib/msgp/gen"
 	"github.com/tinylib/msgp/parse"
@@ -9,7 +9,6 @@ import (
 	"golang.org/x/tools/imports"
 	"io"
 	"io/ioutil"
-	"os"
 	"strings"
 )
 
@@ -21,98 +20,82 @@ func infof(s string, v ...interface{}) {
 // of elements to the given file name and canonical
 // package path.
 func PrintFile(file string, f *parse.FileSet, mode gen.Method) error {
-	err := generate(file, f, mode)
+	out, tests, err := generate(f, mode)
 	if err != nil {
 		return err
 	}
-	infof(">>> Generated \"%s\"\n", file)
-	err = format(file)
+
+	// we'll run goimports on the main file
+	// in another goroutine, and run it here
+	// for the test file. empirically, this
+	// takes about the same amount of time as
+	// doing them in serial when GOMAXPROCS=1,
+	// and faster otherwise.
+	res := goformat(file, out.Bytes())
+	if tests != nil {
+		testfile := strings.TrimSuffix(file, ".go") + "_test.go"
+		err = format(testfile, tests.Bytes())
+		if err != nil {
+			return err
+		}
+		infof(">>> Wrote and formatted \"%s\"\n", testfile)
+	}
+	err = <-res
 	if err != nil {
 		return err
 	}
-	infof(">>> Formatted \"%s\"\n", file)
 	infof(">>> Done.\n")
 	return nil
 }
 
-func format(file string) error {
-	data, err := ioutil.ReadFile(file)
+func format(file string, data []byte) error {
+	out, err := imports.Process(file, data, nil)
 	if err != nil {
 		return err
 	}
-	data, err = imports.Process(file, data, nil)
-	if err != nil {
-		return err
-	}
-	return ioutil.WriteFile(file, data, 0600)
+	return ioutil.WriteFile(file, out, 0600)
 }
 
-func generate(file string, f *parse.FileSet, mode gen.Method) error {
-	if mode&^gen.Test == 0 {
-		return nil
-	}
+func goformat(file string, data []byte) <-chan error {
+	out := make(chan error, 1)
+	go func(file string, data []byte, end chan error) {
+		end <- format(file, data)
+		infof(">>> Wrote and formatted \"%s\"\n", file)
+	}(file, data, out)
+	return out
+}
 
-	outfile, err := os.Create(file)
-	if err != nil {
-		return err
-	}
-	defer outfile.Close()
-	outwr := bufio.NewWriter(outfile)
-	defer outwr.Flush()
+func generate(f *parse.FileSet, mode gen.Method) (*bytes.Buffer, *bytes.Buffer, error) {
+	outbuf := bytes.NewBuffer(make([]byte, 0, 4096))
+	writePkgHeader(outbuf, f.Package)
+	writeImportHeader(outbuf, "github.com/tinylib/msgp/msgp")
 
-	err = writePkgHeader(outwr, f.Package)
-	if err != nil {
-		return err
-	}
-	err = writeImportHeader(outwr, "github.com/tinylib/msgp/msgp")
-	if err != nil {
-		return err
-	}
-
-	var testwr *bufio.Writer
+	var testbuf *bytes.Buffer
+	var testwr io.Writer
 	if mode&gen.Test == gen.Test {
-		tfname := strings.TrimSuffix(file, ".go") + "_test.go"
-		testfile, err := os.Create(strings.TrimSuffix(file, ".go") + "_test.go")
-		if err != nil {
-			return err
-		}
-		infof(">>> Tests in \"%s\"\n", tfname)
-		defer testfile.Close()
-		testwr = bufio.NewWriter(testfile)
-		defer testwr.Flush()
-		err = writePkgHeader(testwr, f.Package)
-		if err != nil {
-			return err
-		}
+		testbuf = bytes.NewBuffer(make([]byte, 0, 4096))
+		writePkgHeader(testbuf, f.Package)
 		if mode&(gen.Encode|gen.Decode) != 0 {
-			err = writeImportHeader(testwr, "bytes", "github.com/tinylib/msgp/msgp", "testing")
+			writeImportHeader(testbuf, "bytes", "github.com/tinylib/msgp/msgp", "testing")
 		} else {
-			err = writeImportHeader(testwr, "github.com/tinylib/msgp/msgp", "testing")
+			writeImportHeader(testbuf, "github.com/tinylib/msgp/msgp", "testing")
 		}
+		testwr = testbuf
 	}
-	return f.PrintTo(gen.NewPrinter(mode, outwr, testwr))
+	return outbuf, testbuf, f.PrintTo(gen.NewPrinter(mode, outbuf, testwr))
 }
 
-func writePkgHeader(w io.Writer, name string) error {
-	_, err := fmt.Fprintln(w, "package", name, "\n")
-	if err != nil {
-		return err
-	}
-	_, err = io.WriteString(w, "// NOTE: THIS FILE WAS PRODUCED BY THE\n// MSGP CODE GENERATION TOOL (github.com/tinylib/msgp)\n// DO NOT EDIT\n\n")
-	return err
+func writePkgHeader(b *bytes.Buffer, name string) {
+	b.WriteString("package ")
+	b.WriteString(name)
+	b.WriteByte('\n')
+	b.WriteString("// NOTE: THIS FILE WAS PRODUCED BY THE\n// MSGP CODE GENERATION TOOL (github.com/tinylib/msgp)\n// DO NOT EDIT\n\n")
 }
 
-func writeImportHeader(w io.Writer, imports ...string) error {
-	_, err := io.WriteString(w, "import (\n")
-	if err != nil {
-		return err
-	}
+func writeImportHeader(b *bytes.Buffer, imports ...string) {
+	b.WriteString("import (\n")
 	for _, im := range imports {
-		_, err = io.WriteString(w, fmt.Sprintf("\t%q\n", im))
-		if err != nil {
-			return err
-		}
+		fmt.Fprintf(b, "\t%q\n", im)
 	}
-	_, err = io.WriteString(w, ")\n\n")
-	return err
+	b.WriteString(")\n\n")
 }