diff --git a/errors.go b/errors.go
index 1c3c713..18a9e68 100644
--- a/errors.go
+++ b/errors.go
@@ -1,15 +1,16 @@
 // Package errors implements functions to manipulate errors.
 package errors
 
-type errorString string
-
-func (e errorString) Error() string {
-	return string(e)
-}
+import "fmt"
 
 // New returns an error that formats as the given text.
 func New(text string) error {
-	return errorString(text)
+	return Errorf(text)
+}
+
+// Errorf returns a formatted error.
+func Errorf(format string, args ...interface{}) error {
+	return fmt.Errorf(format, args...)
 }
 
 // Cause returns the underlying cause of the error, if possible.
@@ -26,9 +27,10 @@
 	if err == nil {
 		return nil
 	}
-	if err, ok := err.(interface {
+	type causer interface {
 		Cause() error
-	}); ok {
+	}
+	if err, ok := err.(causer); ok {
 		return err.Cause()
 	}
 	return err
diff --git a/errors_test.go b/errors_test.go
index e024b5d..7c094c4 100644
--- a/errors_test.go
+++ b/errors_test.go
@@ -1,6 +1,7 @@
 package errors
 
 import (
+	"fmt"
 	"io"
 	"reflect"
 	"testing"
@@ -8,7 +9,7 @@
 
 func TestNew(t *testing.T) {
 	got := New("test error")
-	want := errorString("test error")
+	want := fmt.Errorf("test error")
 
 	if !reflect.DeepEqual(got, want) {
 		t.Errorf("New: got %#v, want %#v", got, want)
@@ -20,8 +21,8 @@
 		err  string
 		want error
 	}{
-		{"", errorString("")},
-		{"foo", errorString("foo")},
+		{"", fmt.Errorf("")},
+		{"foo", fmt.Errorf("foo")},
 		{"foo", New("foo")},
 	}
 
@@ -42,7 +43,7 @@
 }
 
 func (e *causeError) Error() string { return "cause error" }
-func (e *causeError) Cause() error { return e.cause }
+func (e *causeError) Cause() error  { return e.cause }
 
 func TestCause(t *testing.T) {
 	tests := []struct {