diff --git a/Makefile b/Makefile
index a73a3c9..f6bf95f 100644
--- a/Makefile
+++ b/Makefile
@@ -71,4 +71,6 @@ test-integration:
 	@cd e2e && bash ./test.sh
 prepush: test lint test-integration
 check-api:
-	@api -c api/stun1.txt,api/stun1.12.txt github.com/gortc/stun
+	@api -c api/stun1.txt github.com/gortc/stun
+write-api:
+	@api github.com/gortc/stun > api/stun1.txt
diff --git a/api/stun1.12.txt b/api/stun1.12.txt
deleted file mode 100644
index 7515f16..0000000
--- a/api/stun1.12.txt
+++ /dev/null
@@ -1 +0,0 @@
-pkg github.com/gortc/stun, method (*Message) ForEach(AttrType, func(*Message) error) error
diff --git a/api/stun1.txt b/api/stun1.txt
index 0bd4a88..0e40b31 100644
--- a/api/stun1.txt
+++ b/api/stun1.txt
@@ -103,11 +103,13 @@ pkg github.com/gortc/stun, const MethodSend Method
 pkg github.com/gortc/stun, const TransactionIDSize = 12
 pkg github.com/gortc/stun, const TransactionIDSize ideal-int
 pkg github.com/gortc/stun, func Build(...Setter) (*Message, error)
+pkg github.com/gortc/stun, func CheckOverflow(AttrType, int, int) error
 pkg github.com/gortc/stun, func CheckSize(AttrType, int, int) error
 pkg github.com/gortc/stun, func Decode([]uint8, *Message) error
 pkg github.com/gortc/stun, func Dial(string, string) (*Client, error)
 pkg github.com/gortc/stun, func FingerprintValue([]uint8) uint32
 pkg github.com/gortc/stun, func IsAttrSizeInvalid(error) bool
+pkg github.com/gortc/stun, func IsAttrSizeOverflow(error) bool
 pkg github.com/gortc/stun, func IsMessage([]uint8) bool
 pkg github.com/gortc/stun, func MustBuild(...Setter) *Message
 pkg github.com/gortc/stun, func New() *Message
@@ -146,6 +148,7 @@ pkg github.com/gortc/stun, method (*Message) Contains(AttrType) bool
 pkg github.com/gortc/stun, method (*Message) Decode() error
 pkg github.com/gortc/stun, method (*Message) Encode()
 pkg github.com/gortc/stun, method (*Message) Equal(*Message) bool
+pkg github.com/gortc/stun, method (*Message) ForEach(AttrType, func(*Message) error) error
 pkg github.com/gortc/stun, method (*Message) Get(AttrType) ([]uint8, error)
 pkg github.com/gortc/stun, method (*Message) NewTransactionID() error
 pkg github.com/gortc/stun, method (*Message) Parse(...Getter) error
@@ -169,8 +172,6 @@ pkg github.com/gortc/stun, method (*UnknownAttributes) GetFrom(*Message) error
 pkg github.com/gortc/stun, method (*Username) GetFrom(*Message) error
 pkg github.com/gortc/stun, method (*XORMappedAddress) GetFrom(*Message) error
 pkg github.com/gortc/stun, method (*XORMappedAddress) GetFromAs(*Message, AttrType) error
-pkg github.com/gortc/stun, method (AttrLengthErr) Error() string
-pkg github.com/gortc/stun, method (AttrOverflowErr) Error() string
 pkg github.com/gortc/stun, method (AttrType) Optional() bool
 pkg github.com/gortc/stun, method (AttrType) Required() bool
 pkg github.com/gortc/stun, method (AttrType) String() string
@@ -221,14 +222,6 @@ pkg github.com/gortc/stun, type AgentOptions struct, Handler Handler
 pkg github.com/gortc/stun, type AlternateServer struct
 pkg github.com/gortc/stun, type AlternateServer struct, IP net.IP
 pkg github.com/gortc/stun, type AlternateServer struct, Port int
-pkg github.com/gortc/stun, type AttrLengthErr struct
-pkg github.com/gortc/stun, type AttrLengthErr struct, Attr AttrType
-pkg github.com/gortc/stun, type AttrLengthErr struct, Expected int
-pkg github.com/gortc/stun, type AttrLengthErr struct, Got int
-pkg github.com/gortc/stun, type AttrOverflowErr struct
-pkg github.com/gortc/stun, type AttrOverflowErr struct, Got int
-pkg github.com/gortc/stun, type AttrOverflowErr struct, Max int
-pkg github.com/gortc/stun, type AttrOverflowErr struct, Type AttrType
 pkg github.com/gortc/stun, type AttrType uint16
 pkg github.com/gortc/stun, type Attributes []RawAttribute
 pkg github.com/gortc/stun, type Checker interface { Check }
@@ -309,6 +302,8 @@ pkg github.com/gortc/stun, var BindingSuccess MessageType
 pkg github.com/gortc/stun, var ErrAgentClosed error
 pkg github.com/gortc/stun, var ErrAttrSizeInvalid error
 pkg github.com/gortc/stun, var ErrAttributeNotFound error
+pkg github.com/gortc/stun, var ErrAttributeSizeInvalid error
+pkg github.com/gortc/stun, var ErrAttributeSizeOverflow error
 pkg github.com/gortc/stun, var ErrBadIPLength error
 pkg github.com/gortc/stun, var ErrBadUnknownAttrsSize error
 pkg github.com/gortc/stun, var ErrClientClosed error
diff --git a/attributes.go b/attributes.go
index da48f50..e9aa390 100644
--- a/attributes.go
+++ b/attributes.go
@@ -172,34 +172,6 @@ func (m *Message) Get(t AttrType) ([]byte, error) {
 	return v.Value, nil
 }
 
-// AttrOverflowErr occurs when len(v) > Max.
-type AttrOverflowErr struct {
-	Type AttrType
-	Max  int
-	Got  int
-}
-
-func (e AttrOverflowErr) Error() string {
-	return fmt.Sprintf("incorrect length of %s attribute: %d exceeds maximum %d",
-		e.Type, e.Got, e.Max,
-	)
-}
-
-// AttrLengthErr means that length for attribute is invalid.
-type AttrLengthErr struct {
-	Attr     AttrType
-	Got      int
-	Expected int
-}
-
-func (e AttrLengthErr) Error() string {
-	return fmt.Sprintf("incorrect length of %s attribute: got %d, expected %d",
-		e.Attr,
-		e.Got,
-		e.Expected,
-	)
-}
-
 // STUN aligns attributes on 32-bit boundaries, attributes whose content
 // is not a multiple of 4 bytes are padded with 1, 2, or 3 bytes of
 // padding so that its value contains a multiple of 4 bytes.  The
diff --git a/attributes_debug.go b/attributes_debug.go
new file mode 100644
index 0000000..7bf09af
--- /dev/null
+++ b/attributes_debug.go
@@ -0,0 +1,33 @@
+// +build debug
+
+package stun
+
+import "fmt"
+
+// AttrOverflowErr occurs when len(v) > Max.
+type AttrOverflowErr struct {
+	Type AttrType
+	Max  int
+	Got  int
+}
+
+func (e AttrOverflowErr) Error() string {
+	return fmt.Sprintf("incorrect length of %s attribute: %d exceeds maximum %d",
+		e.Type, e.Got, e.Max,
+	)
+}
+
+// AttrLengthErr means that length for attribute is invalid.
+type AttrLengthErr struct {
+	Attr     AttrType
+	Got      int
+	Expected int
+}
+
+func (e AttrLengthErr) Error() string {
+	return fmt.Sprintf("incorrect length of %s attribute: got %d, expected %d",
+		e.Attr,
+		e.Got,
+		e.Expected,
+	)
+}
diff --git a/attributes_debug_test.go b/attributes_debug_test.go
new file mode 100644
index 0000000..9e03303
--- /dev/null
+++ b/attributes_debug_test.go
@@ -0,0 +1,27 @@
+// +build debug
+
+package stun
+
+import "testing"
+
+func TestAttrOverflowErr_Error(t *testing.T) {
+	err := AttrOverflowErr{
+		Got:  100,
+		Max:  50,
+		Type: AttrLifetime,
+	}
+	if err.Error() != "incorrect length of LIFETIME attribute: 100 exceeds maximum 50" {
+		t.Error("bad error string", err)
+	}
+}
+
+func TestAttrLengthErr_Error(t *testing.T) {
+	err := AttrLengthErr{
+		Attr:     AttrErrorCode,
+		Expected: 15,
+		Got:      99,
+	}
+	if err.Error() != "incorrect length of ERROR-CODE attribute: got 99, expected 15" {
+		t.Errorf("bad error string: %s", err)
+	}
+}
diff --git a/attributes_test.go b/attributes_test.go
index 6dacbd4..d74d3ac 100644
--- a/attributes_test.go
+++ b/attributes_test.go
@@ -69,28 +69,6 @@ func TestPadding(t *testing.T) {
 	}
 }
 
-func TestAttrLengthError_Error(t *testing.T) {
-	err := AttrOverflowErr{
-		Got:  100,
-		Max:  50,
-		Type: AttrLifetime,
-	}
-	if err.Error() != "incorrect length of LIFETIME attribute: 100 exceeds maximum 50" {
-		t.Error("bad error string", err)
-	}
-}
-
-func TestAttrLengthErr_Error(t *testing.T) {
-	err := AttrLengthErr{
-		Attr:     AttrErrorCode,
-		Expected: 15,
-		Got:      99,
-	}
-	if err.Error() != "incorrect length of ERROR-CODE attribute: got 99, expected 15" {
-		t.Errorf("bad error string: %s", err)
-	}
-}
-
 func TestAttrTypeRange(t *testing.T) {
 	for _, a := range []AttrType{
 		AttrPriority,
diff --git a/checks.go b/checks.go
index 6c1b60c..ca58525 100644
--- a/checks.go
+++ b/checks.go
@@ -9,7 +9,7 @@ func CheckSize(_ AttrType, got, expected int) error {
 	if got == expected {
 		return nil
 	}
-	return ErrAttrSizeInvalid
+	return ErrAttributeSizeInvalid
 }
 
 func checkHMAC(got, expected []byte) error {
@@ -28,5 +28,18 @@ func checkFingerprint(got, expected uint32) error {
 
 // IsAttrSizeInvalid returns true if error means that attribute size is invalid.
 func IsAttrSizeInvalid(err error) bool {
-	return err == ErrAttrSizeInvalid
+	return err == ErrAttributeSizeInvalid
+}
+
+// CheckOverflow returns ErrAttributeSizeOverflow if got is bigger that max.
+func CheckOverflow(_ AttrType, got, max int) error {
+	if got <= max {
+		return nil
+	}
+	return ErrAttributeSizeOverflow
+}
+
+// IsAttrSizeOverflow returns true if error means that attribute size is too big.
+func IsAttrSizeOverflow(err error) bool {
+	return err == ErrAttributeSizeOverflow
 }
diff --git a/checks_debug.go b/checks_debug.go
index 1ca503a..1b0b9c3 100644
--- a/checks_debug.go
+++ b/checks_debug.go
@@ -41,3 +41,21 @@ func IsAttrSizeInvalid(err error) bool {
 	_, ok := err.(*AttrLengthErr)
 	return ok
 }
+
+// CheckOverflow returns *AttrOverflowErr if got is bigger that max.
+func CheckOverflow(t AttrType, got, max int) error {
+	if got <= max {
+		return nil
+	}
+	return &AttrOverflowErr{
+		Type: t,
+		Got:  got,
+		Max:  max,
+	}
+}
+
+// IsAttrSizeOverflow returns true if error means that attribute size is too big.
+func IsAttrSizeOverflow(err error) bool {
+	_, ok := err.(*AttrOverflowErr)
+	return ok
+}
diff --git a/errorcode.go b/errorcode.go
index 9b43f00..6b42b7f 100644
--- a/errorcode.go
+++ b/errorcode.go
@@ -30,12 +30,11 @@ const (
 // AddTo adds ERROR-CODE to m.
 func (c ErrorCodeAttribute) AddTo(m *Message) error {
 	value := make([]byte, 0, errorCodeReasonMaxB)
-	if len(c.Reason) > errorCodeReasonMaxB {
-		return &AttrOverflowErr{
-			Got:  len(c.Reason) + errorCodeReasonStart,
-			Max:  errorCodeReasonMaxB + errorCodeReasonStart,
-			Type: AttrErrorCode,
-		}
+	if err := CheckOverflow(AttrErrorCode,
+		len(c.Reason)+errorCodeReasonStart,
+		errorCodeReasonMaxB+errorCodeReasonStart,
+	); err != nil {
+		return err
 	}
 	value = value[:errorCodeReasonStart+len(c.Reason)]
 	number := byte(c.Code % errorCodeModulo) // error code modulo 100
diff --git a/errors.go b/errors.go
index e121dab..7802ce4 100644
--- a/errors.go
+++ b/errors.go
@@ -56,4 +56,12 @@ func newAttrDecodeErr(children, message string) *DecodeErr {
 }
 
 // ErrAttrSizeInvalid means that decoded attribute size is invalid.
+//
+// DEPRECATED: use ErrAttributeSizeInvalid.
 var ErrAttrSizeInvalid = errors.New("attribute size is invalid")
+
+// ErrAttributeSizeInvalid means that decoded attribute size is invalid.
+var ErrAttributeSizeInvalid = ErrAttrSizeInvalid
+
+// ErrAttributeSizeOverflow means that decoded attribute size is too big.
+var ErrAttributeSizeOverflow = errors.New("attribute size overflow")
diff --git a/textattrs.go b/textattrs.go
index c2e75f0..69ca58a 100644
--- a/textattrs.go
+++ b/textattrs.go
@@ -111,12 +111,8 @@ type TextAttribute []byte
 // AddToAs adds attribute with type t to m, checking maximum length. If maxLen
 // is less than 0, no check is performed.
 func (v TextAttribute) AddToAs(m *Message, t AttrType, maxLen int) error {
-	if maxLen > 0 && len(v) > maxLen {
-		return &AttrOverflowErr{
-			Max:  maxLen,
-			Got:  len(v),
-			Type: t,
-		}
+	if err := CheckOverflow(t, len(v), maxLen); err != nil {
+		return err
 	}
 	m.Add(t, v)
 	return nil
diff --git a/textattrs_test.go b/textattrs_test.go
index e06366d..d6e932d 100644
--- a/textattrs_test.go
+++ b/textattrs_test.go
@@ -38,7 +38,7 @@ func TestSoftware_GetFrom(t *testing.T) {
 func TestSoftware_AddTo_Invalid(t *testing.T) {
 	m := New()
 	s := make(Software, 1024)
-	if err, ok := s.AddTo(m).(*AttrOverflowErr); !ok {
+	if err := s.AddTo(m); !IsAttrSizeOverflow(err) {
 		t.Errorf("AddTo should return *AttrOverflowErr, got: %v", err)
 	}
 	if err := s.GetFrom(m); err != ErrAttributeNotFound {
@@ -88,8 +88,8 @@ func TestUsername(t *testing.T) {
 	m.WriteHeader()
 	t.Run("Bad length", func(t *testing.T) {
 		badU := make(Username, 600)
-		if err, ok := badU.AddTo(m).(*AttrOverflowErr); !ok {
-			t.Errorf("expected length error, got %v", err)
+		if err := badU.AddTo(m); !IsAttrSizeOverflow(err) {
+			t.Errorf("AddTo should return *AttrOverflowErr, got: %v", err)
 		}
 	})
 	t.Run("AddTo", func(t *testing.T) {
@@ -164,7 +164,7 @@ func TestRealm_GetFrom(t *testing.T) {
 func TestRealm_AddTo_Invalid(t *testing.T) {
 	m := New()
 	r := make(Realm, 1024)
-	if err, ok := r.AddTo(m).(*AttrOverflowErr); !ok || err.Type != AttrRealm {
+	if err := r.AddTo(m); !IsAttrSizeOverflow(err) {
 		t.Errorf("AddTo should return *AttrOverflowErr, got: %v", err)
 	}
 	if err := r.GetFrom(m); err != ErrAttributeNotFound {
@@ -205,7 +205,7 @@ func TestNonce_GetFrom(t *testing.T) {
 func TestNonce_AddTo_Invalid(t *testing.T) {
 	m := New()
 	n := make(Nonce, 1024)
-	if err, ok := n.AddTo(m).(*AttrOverflowErr); !ok || err.Type != AttrNonce {
+	if err := n.AddTo(m); !IsAttrSizeOverflow(err) {
 		t.Errorf("AddTo should return *AttrOverflowErr, got: %v", err)
 	}
 	if err := n.GetFrom(m); err != ErrAttributeNotFound {
diff --git a/xoraddr.go b/xoraddr.go
index 78d1693..23f7777 100644
--- a/xoraddr.go
+++ b/xoraddr.go
@@ -108,12 +108,8 @@ func (a *XORMappedAddress) GetFromAs(m *Message, t AttrType) error {
 	if len(v) <= 4 {
 		return io.ErrUnexpectedEOF
 	}
-	if len(v[4:]) > len(a.IP) {
-		return &AttrOverflowErr{
-			Got:  len(v[4:]),
-			Type: AttrXORMappedAddress,
-			Max:  len(a.IP),
-		}
+	if err := CheckOverflow(t, len(v[4:]), len(a.IP)); err != nil {
+		return err
 	}
 	a.Port = int(bin.Uint16(v[2:4])) ^ (magicCookie >> 16)
 	xorValue := make([]byte, 4+TransactionIDSize)
diff --git a/xoraddr_test.go b/xoraddr_test.go
index a3d92f5..f78a286 100644
--- a/xoraddr_test.go
+++ b/xoraddr_test.go
@@ -80,11 +80,8 @@ func TestXORMappedAddress_GetFrom(t *testing.T) {
 		// {0, 1} is correct addr family.
 		m.Add(AttrXORMappedAddress, []byte{0, 1, 3, 4, 5, 6, 7, 8, 9, 1, 1, 1, 1, 1, 2, 3, 4})
 		addr := new(XORMappedAddress)
-		err := addr.GetFrom(m)
-		if _, ok := err.(*AttrOverflowErr); !ok {
-			t.Errorf("should render AttrOverflowErr error, got <%s> (%T)",
-				err, err,
-			)
+		if err := addr.GetFrom(m); !IsAttrSizeOverflow(err) {
+			t.Errorf("AddTo should return *AttrOverflowErr, got: %v", err)
 		}
 	})
 }