diff --git a/encode.go b/encode.go
index b45147f5..ebef78f1 100644
--- a/encode.go
+++ b/encode.go
@@ -1648,8 +1648,21 @@ func encodeTag(e *bytes.Buffer, em *encMode, v reflect.Value) error {
 	// Marshal tag number
 	encodeHead(e, byte(cborTypeTag), t.Number)
 
+	vem := *em // shallow copy
+
+	// For built-in tags, disable settings that may introduce tag validity errors when
+	// marshaling certain Content values.
+	switch t.Number {
+	case tagNumRFC3339Time:
+		vem.stringType = StringToTextString
+		vem.stringMajorType = cborTypeTextString
+	case tagNumUnsignedBignum, tagNumNegativeBignum:
+		vem.byteSlice = ByteSliceToByteString
+		vem.byteSliceEncodingTag = 0
+	}
+
 	// Marshal tag content
-	return encode(e, em, reflect.ValueOf(t.Content))
+	return encode(e, &vem, reflect.ValueOf(t.Content))
 }
 
 // encodeHead writes CBOR head of specified type t and returns number of bytes written.
diff --git a/tag.go b/tag.go
index 4c9c99f8..5c4d2b7a 100644
--- a/tag.go
+++ b/tag.go
@@ -7,7 +7,9 @@ import (
 	"sync"
 )
 
-// Tag represents CBOR tag data, including tag number and unmarshaled tag content.
+// Tag represents CBOR tag data, including tag number and unmarshaled tag content. Marshaling and
+// unmarshaling of tag content is subject to any encode and decode options that would apply to
+// enclosed data item if it were to appear outside of a tag.
 type Tag struct {
 	Number  uint64
 	Content interface{}
diff --git a/tag_test.go b/tag_test.go
index fd9246d1..f5917c4f 100644
--- a/tag_test.go
+++ b/tag_test.go
@@ -1490,3 +1490,49 @@ func TestMarshalRawTagContainingMalformedCBORData(t *testing.T) {
 		})
 	}
 }
+
+// TestEncodeBuiltinTag tests that marshaling a value of type Tag "does the right thing" when
+// marshaling the enclosed data item of a built-in tag number.
+func TestEncodeBuiltinTag(t *testing.T) {
+	for _, tc := range []struct {
+		name string
+		tag  Tag
+		opts EncOptions
+		want []byte
+	}{
+		{
+			name: "unsigned bignum content not enclosed in expected encoding tag",
+			tag:  Tag{Number: tagNumUnsignedBignum, Content: []byte{0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}},
+			opts: EncOptions{ByteSlice: ByteSliceExpectedEncodingBase16},
+			want: []byte{0xc2, 0x49, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
+		},
+		{
+			name: "negative bignum content not enclosed in expected encoding tag",
+			tag:  Tag{Number: tagNumNegativeBignum, Content: []byte{0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}},
+			opts: EncOptions{ByteSlice: ByteSliceExpectedEncodingBase16},
+			want: []byte{0xc3, 0x49, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00},
+		},
+		{
+			name: "rfc 3339 content is not encoded as byte string",
+			tag:  Tag{Number: tagNumRFC3339Time, Content: "2013-03-21T20:04:00Z"},
+			opts: EncOptions{String: StringToByteString},
+			want: hexDecode("c074323031332d30332d32315432303a30343a30305a"),
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			em, err := tc.opts.EncMode()
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			got, err := em.Marshal(tc.tag)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if !bytes.Equal(got, tc.want) {
+				t.Errorf("unexpected difference\ngot: 0x%x\nwant: 0x%x", got, tc.want)
+			}
+		})
+	}
+}