diff --git a/pkg/bitio/bitio.go b/pkg/bitio/bitio.go
index 73bdeae4..4ffd72ae 100644
--- a/pkg/bitio/bitio.go
+++ b/pkg/bitio/bitio.go
@@ -8,6 +8,9 @@ import (
 	"io"
 )
 
+var ErrOffset = errors.New("invalid seek offset")
+var ErrNegativeNBits = errors.New("negative number of bits")
+
 type BitReaderAt interface {
 	ReadBitsAt(p []byte, nBits int, bitOff int64) (n int, err error)
 }
@@ -114,6 +117,10 @@ func BitsByteCount(nBits int64) int64 {
 }
 
 func readFull(p []byte, nBits int, bitOff int64, fn func(p []byte, nBits int, bitOff int64) (int, error)) (int, error) {
+	if nBits < 0 {
+		return 0, ErrNegativeNBits
+	}
+
 	readBitOffset := 0
 	for readBitOffset < nBits {
 		byteOffset := readBitOffset / 8
@@ -180,7 +187,6 @@ func EndPos(rs BitSeeker) (int64, error) {
 }
 
 // Reader is a BitReadSeeker and BitReaderAt reading from a io.ReadSeeker
-// TODO: private?
 type Reader struct {
 	bitPos int64
 	rs     io.ReadSeeker
@@ -195,6 +201,10 @@ func NewReaderFromReadSeeker(rs io.ReadSeeker) *Reader {
 }
 
 func (r *Reader) ReadBitsAt(p []byte, nBits int, bitOffset int64) (int, error) {
+	if nBits < 0 {
+		return 0, ErrNegativeNBits
+	}
+
 	readBytePos := bitOffset / 8
 	readSkipBits := int(bitOffset % 8)
 	wantReadBits := readSkipBits + nBits
@@ -311,8 +321,6 @@ func (r *SectionBitReader) ReadBits(p []byte, nBits int) (n int, err error) {
 	return rBits, err
 }
 
-var errOffset = errors.New("invalid seek offset")
-
 func (r *SectionBitReader) SeekBits(bitOff int64, whence int) (int64, error) {
 	switch whence {
 	case io.SeekStart:
@@ -325,7 +333,7 @@ func (r *SectionBitReader) SeekBits(bitOff int64, whence int) (int64, error) {
 		panic("unknown whence")
 	}
 	if bitOff < r.bitBase {
-		return 0, errOffset
+		return 0, ErrOffset
 	}
 	r.bitOff = bitOff
 	return bitOff - r.bitBase, nil
@@ -411,7 +419,7 @@ func (m *MultiBitReader) SeekBits(bitOff int64, whence int) (int64, error) {
 		panic("unknown whence")
 	}
 	if p < 0 || p > end {
-		return 0, errOffset
+		return 0, ErrOffset
 	}
 
 	m.pos = p
diff --git a/pkg/bitio/rw64.go b/pkg/bitio/rw64.go
index ddaa8a4c..4e562539 100644
--- a/pkg/bitio/rw64.go
+++ b/pkg/bitio/rw64.go
@@ -8,8 +8,8 @@ import (
 // Read64 read nBits bits large unsigned integer from buf starting from firstBit.
 // Integer is read most significant bit first.
 func Read64(buf []byte, firstBit int, nBits int) uint64 {
-	if nBits > 64 {
-		panic(fmt.Sprintf("only supports =< 64 bits (%d)", nBits))
+	if nBits < 0 || nBits > 64 {
+		panic(fmt.Sprintf("nBits must be 0-64 (%d)", nBits))
 	}
 
 	be := binary.BigEndian
@@ -91,8 +91,8 @@ func Read64(buf []byte, firstBit int, nBits int) uint64 {
 }
 
 func Write64(v uint64, nBits int, buf []byte, firstBit int) {
-	if nBits > 64 {
-		panic(fmt.Sprintf("only supports =< 64 bits (%d)", nBits))
+	if nBits < 0 || nBits > 64 {
+		panic(fmt.Sprintf("nBits must be 0-64 (%d)", nBits))
 	}
 
 	be := binary.BigEndian
diff --git a/pkg/decode/numbers.go b/pkg/decode/numbers.go
index 98ebaf18..cb4d89ec 100644
--- a/pkg/decode/numbers.go
+++ b/pkg/decode/numbers.go
@@ -37,6 +37,9 @@ func (d *D) TrySE(nBits int, endian Endian) (int64, error) {
 	if err != nil {
 		return 0, err
 	}
+	if nBits == 0 {
+		return 0, nil
+	}
 	if endian == LittleEndian {
 		n = bitio.Uint64ReverseBytes(nBits, n)
 	}