diff --git a/code/code.go b/code/code.go
index 09731861..4a2ad0cd 100644
--- a/code/code.go
+++ b/code/code.go
@@ -36,8 +36,8 @@ type ErrCoder interface {
 // It also satisfies the ErrCoder interface, allowing the code to be recovered.
 type codeError Code
 
-// Error satisfies the error interface using the registered string for the
-// code, if one is defined, or else a placeholder that describes the value.
+// Error satisfies the error interface using the built-in string for the code,
+// if one is defined, or else a placeholder that describes the value.
 func (c codeError) Error() string { return Code(c).String() }
 
 // ErrCode trivially satisfies the ErrCoder interface.
@@ -51,7 +51,7 @@ func (c codeError) Is(err error) bool {
 
 // Err converts c to an error value, which is nil for code.NoError and
 // otherwise an error value whose code is c and whose text is based on the
-// registered string for c if one exists.
+// built-in string for c if one exists.
 func (c Code) Err() error {
 	if c == NoError {
 		return nil
@@ -88,22 +88,6 @@ var stdError = map[Code]string{
 	DeadlineExceeded: "deadline exceeded",
 }
 
-// Register adds a new Code value with the specified message string.  This
-// function will panic if the proposed value is already registered with a
-// different string.
-//
-// Registering a code allows you to control the string returned by the String
-// method for the code value you specify.  It is not necessary to register a
-// code before using it. An unregistered code renders a generic string.
-func Register(value int32, message string) Code {
-	code := Code(value)
-	if s, ok := stdError[code]; ok && s != message {
-		panic(fmt.Sprintf("code %d is already registered for %q", code, s))
-	}
-	stdError[code] = message
-	return code
-}
-
 // FromError returns a Code to categorize the specified error.
 // If err == nil, it returns code.NoError.
 // If err is (or wraps) an ErrCoder, it returns the reported code value.
diff --git a/code/code_test.go b/code/code_test.go
index cf0c6ed6..1b3c202d 100644
--- a/code/code_test.go
+++ b/code/code_test.go
@@ -12,27 +12,6 @@ import (
 	"github.com/creachadair/jrpc2/code"
 )
 
-func TestRegistration(t *testing.T) {
-	const message = "fun for the whole family"
-	c := code.Register(-100, message)
-	if got := c.String(); got != message {
-		t.Errorf("Register(-100): got %q, want %q", got, message)
-	} else if c != -100 {
-		t.Errorf("Register(-100): got %d instead", c)
-	}
-}
-
-func TestRegistrationError(t *testing.T) {
-	defer func() {
-		if v := recover(); v != nil {
-			t.Logf("Register correctly panicked: %v", v)
-		} else {
-			t.Fatalf("Register should have panicked on input %d, but did not", code.ParseError)
-		}
-	}()
-	code.Register(int32(code.ParseError), "bogus")
-}
-
 type testCoder code.Code
 
 func (t testCoder) ErrCode() code.Code { return code.Code(t) }
@@ -91,12 +70,10 @@ func TestErr(t *testing.T) {
 		code code.Code
 		want error
 	}
-	code.Register(1, "look for the bear necessities")
-	code.Register(2, "the simple bear necessities")
 	tests := []test{
 		{code.NoError, nil},
 		{0, errors.New("error code 0")},
-		{1, errors.New("look for the bear necessities")},
+		{1, errors.New("error code 1")},
 		{-17, errors.New("error code -17")},
 	}