diff --git a/cid.go b/cid.go
index 9f8c87d8..21d6fb80 100644
--- a/cid.go
+++ b/cid.go
@@ -1,11 +1,7 @@
 package pgtype
 
 import (
-	"fmt"
 	"io"
-	"strconv"
-
-	"github.com/jackc/pgx/pgio"
 )
 
 // CID is PostgreSQL's Command Identifier type.
@@ -19,123 +15,33 @@ import (
 // It is currently implemented as an unsigned four byte integer.
 // Its definition can be found in src/include/c.h as CommandId
 // in the PostgreSQL sources.
-type CID struct {
-	Uint   uint32
-	Status Status
-}
+type CID pguint32
 
 // ConvertFrom converts from src to dst. Note that as CID is not a general
 // number type ConvertFrom does not do automatic type conversion as other number
 // types do.
 func (dst *CID) ConvertFrom(src interface{}) error {
-	switch value := src.(type) {
-	case CID:
-		*dst = value
-	case uint32:
-		*dst = CID{Uint: value, Status: Present}
-	default:
-		return fmt.Errorf("cannot convert %v to CID", value)
-	}
-
-	return nil
+	return (*pguint32)(dst).ConvertFrom(src)
 }
 
 // AssignTo assigns from src to dst. Note that as CID is not a general number
 // type AssignTo does not do automatic type conversion as other number types do.
 func (src *CID) AssignTo(dst interface{}) error {
-	switch v := dst.(type) {
-	case *uint32:
-		if src.Status == Present {
-			*v = src.Uint
-		} else {
-			return fmt.Errorf("cannot assign %v into %T", src, dst)
-		}
-	case **uint32:
-		if src.Status == Present {
-			n := src.Uint
-			*v = &n
-		} else {
-			*v = nil
-		}
-	}
-
-	return nil
+	return (*pguint32)(src).AssignTo(dst)
 }
 
 func (dst *CID) DecodeText(r io.Reader) error {
-	size, err := pgio.ReadInt32(r)
-	if err != nil {
-		return err
-	}
-
-	if size == -1 {
-		*dst = CID{Status: Null}
-		return nil
-	}
-
-	buf := make([]byte, int(size))
-	_, err = r.Read(buf)
-	if err != nil {
-		return err
-	}
-
-	n, err := strconv.ParseUint(string(buf), 10, 32)
-	if err != nil {
-		return err
-	}
-
-	*dst = CID{Uint: uint32(n), Status: Present}
-	return nil
+	return (*pguint32)(dst).DecodeText(r)
 }
 
 func (dst *CID) DecodeBinary(r io.Reader) error {
-	size, err := pgio.ReadInt32(r)
-	if err != nil {
-		return err
-	}
-
-	if size == -1 {
-		*dst = CID{Status: Null}
-		return nil
-	}
-
-	if size != 4 {
-		return fmt.Errorf("invalid length for cid: %v", size)
-	}
-
-	n, err := pgio.ReadUint32(r)
-	if err != nil {
-		return err
-	}
-
-	*dst = CID{Uint: n, Status: Present}
-	return nil
+	return (*pguint32)(dst).DecodeBinary(r)
 }
 
 func (src CID) EncodeText(w io.Writer) error {
-	if done, err := encodeNotPresent(w, src.Status); done {
-		return err
-	}
-
-	s := strconv.FormatUint(uint64(src.Uint), 10)
-	_, err := pgio.WriteInt32(w, int32(len(s)))
-	if err != nil {
-		return nil
-	}
-	_, err = w.Write([]byte(s))
-	return err
+	return (pguint32)(src).EncodeText(w)
 }
 
 func (src CID) EncodeBinary(w io.Writer) error {
-	if done, err := encodeNotPresent(w, src.Status); done {
-		return err
-	}
-
-	_, err := pgio.WriteInt32(w, 4)
-	if err != nil {
-		return err
-	}
-
-	_, err = pgio.WriteUint32(w, src.Uint)
-	return err
+	return (pguint32)(src).EncodeBinary(w)
 }
diff --git a/pguint32.go b/pguint32.go
new file mode 100644
index 00000000..66b385fb
--- /dev/null
+++ b/pguint32.go
@@ -0,0 +1,130 @@
+package pgtype
+
+import (
+	"fmt"
+	"io"
+	"strconv"
+
+	"github.com/jackc/pgx/pgio"
+)
+
+// pguint32 is the core type that is used to implement PostgreSQL types such as
+// CID and XID.
+type pguint32 struct {
+	Uint   uint32
+	Status Status
+}
+
+// ConvertFrom converts from src to dst. Note that as pguint32 is not a general
+// number type ConvertFrom does not do automatic type conversion as other number
+// types do.
+func (dst *pguint32) ConvertFrom(src interface{}) error {
+	switch value := src.(type) {
+	case uint32:
+		*dst = pguint32{Uint: value, Status: Present}
+	default:
+		return fmt.Errorf("cannot convert %v to pguint32", value)
+	}
+
+	return nil
+}
+
+// AssignTo assigns from src to dst. Note that as pguint32 is not a general number
+// type AssignTo does not do automatic type conversion as other number types do.
+func (src *pguint32) AssignTo(dst interface{}) error {
+	switch v := dst.(type) {
+	case *uint32:
+		if src.Status == Present {
+			*v = src.Uint
+		} else {
+			return fmt.Errorf("cannot assign %v into %T", src, dst)
+		}
+	case **uint32:
+		if src.Status == Present {
+			n := src.Uint
+			*v = &n
+		} else {
+			*v = nil
+		}
+	}
+
+	return nil
+}
+
+func (dst *pguint32) DecodeText(r io.Reader) error {
+	size, err := pgio.ReadInt32(r)
+	if err != nil {
+		return err
+	}
+
+	if size == -1 {
+		*dst = pguint32{Status: Null}
+		return nil
+	}
+
+	buf := make([]byte, int(size))
+	_, err = r.Read(buf)
+	if err != nil {
+		return err
+	}
+
+	n, err := strconv.ParseUint(string(buf), 10, 32)
+	if err != nil {
+		return err
+	}
+
+	*dst = pguint32{Uint: uint32(n), Status: Present}
+	return nil
+}
+
+func (dst *pguint32) DecodeBinary(r io.Reader) error {
+	size, err := pgio.ReadInt32(r)
+	if err != nil {
+		return err
+	}
+
+	if size == -1 {
+		*dst = pguint32{Status: Null}
+		return nil
+	}
+
+	if size != 4 {
+		return fmt.Errorf("invalid length for cid: %v", size)
+	}
+
+	n, err := pgio.ReadUint32(r)
+	if err != nil {
+		return err
+	}
+
+	*dst = pguint32{Uint: n, Status: Present}
+	return nil
+}
+
+func (src pguint32) EncodeText(w io.Writer) error {
+	if done, err := encodeNotPresent(w, src.Status); done {
+		return err
+	}
+
+	s := strconv.FormatUint(uint64(src.Uint), 10)
+	_, err := pgio.WriteInt32(w, int32(len(s)))
+	if err != nil {
+		return nil
+	}
+	_, err = w.Write([]byte(s))
+	return err
+}
+
+func (src pguint32) EncodeBinary(w io.Writer) error {
+	if done, err := encodeNotPresent(w, src.Status); done {
+		return err
+	}
+
+	_, err := pgio.WriteInt32(w, 4)
+	if err != nil {
+		return err
+	}
+
+	_, err = pgio.WriteUint32(w, src.Uint)
+	return err
+}
diff --git a/xid.go b/xid.go
index f4d087a5..b311cbfb 100644
--- a/xid.go
+++ b/xid.go
@@ -18,28 +18,33 @@ import (
 // It is currently implemented as an unsigned four byte integer.
 // Its definition can be found in src/include/postgres_ext.h as TransactionId
 // in the PostgreSQL sources.
-type XID CID
+type XID pguint32
 
+// ConvertFrom converts from src to dst. Note that as XID is not a general
+// number type ConvertFrom does not do automatic type conversion as other number
+// types do.
 func (dst *XID) ConvertFrom(src interface{}) error {
-	return (*CID)(dst).ConvertFrom(src)
+	return (*pguint32)(dst).ConvertFrom(src)
 }
 
+// AssignTo assigns from src to dst. Note that as XID is not a general number
+// type AssignTo does not do automatic type conversion as other number types do.
 func (src *XID) AssignTo(dst interface{}) error {
-	return (*CID)(src).AssignTo(dst)
+	return (*pguint32)(src).AssignTo(dst)
 }
 
 func (dst *XID) DecodeText(r io.Reader) error {
-	return (*CID)(dst).DecodeText(r)
+	return (*pguint32)(dst).DecodeText(r)
 }
 
 func (dst *XID) DecodeBinary(r io.Reader) error {
-	return (*CID)(dst).DecodeBinary(r)
+	return (*pguint32)(dst).DecodeBinary(r)
 }
 
 func (src XID) EncodeText(w io.Writer) error {
-	return (CID)(src).EncodeText(w)
+	return (pguint32)(src).EncodeText(w)
 }
 
 func (src XID) EncodeBinary(w io.Writer) error {
-	return (CID)(src).EncodeBinary(w)
+	return (pguint32)(src).EncodeBinary(w)
 }