diff --git a/s2/decode.go b/s2/decode.go
index 039ddb911b..605b85dd91 100644
--- a/s2/decode.go
+++ b/s2/decode.go
@@ -77,10 +77,38 @@ func Decode(dst, src []byte) ([]byte, error) {
 // NewReader returns a new Reader that decompresses from r, using the framing
 // format described at
 // https://github.com/google/snappy/blob/master/framing_format.txt with S2 changes.
-func NewReader(r io.Reader) *Reader {
-	return &Reader{
-		r:   r,
-		buf: make([]byte, MaxEncodedLen(maxBlockSize)+checksumSize),
+func NewReader(r io.Reader, opts ...ReaderOption) *Reader {
+	nr := Reader{
+		r:        r,
+		maxBlock: maxBlockSize,
+	}
+	for _, opt := range opts {
+		if err := opt(&nr); err != nil {
+			nr.err = err
+			return &nr
+		}
+	}
+	nr.buf = make([]byte, MaxEncodedLen(nr.maxBlock)+checksumSize)
+	nr.paramsOK = true
+	return &nr
+}
+
+// ReaderOption is an option for creating a decoder.
+type ReaderOption func(*Reader) error
+
+// ReaderMaxBlockSize allows to control allocations if the stream
+// has been compressed with a smaller WriterBlockSize, or with the default 1MB.
+// Blocks must be this size or smaller to decompress,
+// otherwise the decoder will return ErrUnsupported.
+//
+// Default is the maximum limit of 4MB.
+func ReaderMaxBlockSize(n int) ReaderOption {
+	return func(r *Reader) error {
+		if n > maxBlockSize || n <= 0 {
+			return errors.New("s2: block size too large. Must be <= 4MB and > 0")
+		}
+		r.maxBlock = n
+		return nil
 	}
 }
 
@@ -92,13 +120,18 @@ type Reader struct {
 	buf     []byte
 	// decoded[i:j] contains decoded bytes that have not yet been passed on.
 	i, j       int
+	maxBlock   int
 	readHeader bool
+	paramsOK   bool
 }
 
 // Reset discards any buffered data, resets all state, and switches the Snappy
 // reader to read from r. This permits reusing a Reader rather than allocating
 // a new one.
 func (r *Reader) Reset(reader io.Reader) {
+	if !r.paramsOK {
+		return
+	}
 	r.r = reader
 	r.err = nil
 	r.i = 0
@@ -116,6 +149,36 @@ func (r *Reader) readFull(p []byte, allowEOF bool) (ok bool) {
 	return true
 }
 
+// skipN will skip n bytes.
+// If the supplied reader supports seeking that is used.
+// tmp is used as a temporary buffer for reading.
+// The supplied slice does not need to be the size of the read.
+func (r *Reader) skipN(tmp []byte, n int, allowEOF bool) (ok bool) {
+	if rs, ok := r.r.(io.ReadSeeker); ok {
+		_, err := rs.Seek(int64(n), io.SeekCurrent)
+		if err == nil {
+			return true
+		}
+		if err == io.ErrUnexpectedEOF || (r.err == io.EOF && !allowEOF) {
+			r.err = ErrCorrupt
+			return false
+		}
+	}
+	for n > 0 {
+		if n < len(tmp) {
+			tmp = tmp[:n]
+		}
+		if _, r.err = io.ReadFull(r.r, tmp); r.err != nil {
+			if r.err == io.ErrUnexpectedEOF || (r.err == io.EOF && !allowEOF) {
+				r.err = ErrCorrupt
+			}
+			return false
+		}
+		n -= len(tmp)
+	}
+	return true
+}
+
 // Read satisfies the io.Reader interface.
 func (r *Reader) Read(p []byte) (int, error) {
 	if r.err != nil {
@@ -139,10 +202,6 @@ func (r *Reader) Read(p []byte) (int, error) {
 			r.readHeader = true
 		}
 		chunkLen := int(r.buf[1]) | int(r.buf[2])<<8 | int(r.buf[3])<<16
-		if chunkLen > len(r.buf) {
-			r.err = ErrUnsupported
-			return 0, r.err
-		}
 
 		// The chunk types are specified at
 		// https://github.com/google/snappy/blob/master/framing_format.txt
@@ -153,6 +212,10 @@ func (r *Reader) Read(p []byte) (int, error) {
 				r.err = ErrCorrupt
 				return 0, r.err
 			}
+			if chunkLen > len(r.buf) {
+				r.err = ErrUnsupported
+				return 0, r.err
+			}
 			buf := r.buf[:chunkLen]
 			if !r.readFull(buf, false) {
 				return 0, r.err
@@ -166,7 +229,7 @@ func (r *Reader) Read(p []byte) (int, error) {
 				return 0, r.err
 			}
 			if n > len(r.decoded) {
-				if n > maxBlockSize {
+				if n > r.maxBlock {
 					r.err = ErrCorrupt
 					return 0, r.err
 				}
@@ -189,6 +252,10 @@ func (r *Reader) Read(p []byte) (int, error) {
 				r.err = ErrCorrupt
 				return 0, r.err
 			}
+			if chunkLen > len(r.buf) {
+				r.err = ErrUnsupported
+				return 0, r.err
+			}
 			buf := r.buf[:checksumSize]
 			if !r.readFull(buf, false) {
 				return 0, r.err
@@ -197,7 +264,7 @@ func (r *Reader) Read(p []byte) (int, error) {
 			// Read directly into r.decoded instead of via r.buf.
 			n := chunkLen - checksumSize
 			if n > len(r.decoded) {
-				if n > maxBlockSize {
+				if n > r.maxBlock {
 					r.err = ErrCorrupt
 					return 0, r.err
 				}
@@ -238,7 +305,12 @@ func (r *Reader) Read(p []byte) (int, error) {
 		}
 		// Section 4.4 Padding (chunk type 0xfe).
 		// Section 4.6. Reserved skippable chunks (chunk types 0x80-0xfd).
-		if !r.readFull(r.buf[:chunkLen], false) {
+		if chunkLen > maxBlockSize {
+			r.err = ErrUnsupported
+			return 0, r.err
+		}
+
+		if !r.skipN(r.buf, chunkLen, false) {
 			return 0, r.err
 		}
 	}
@@ -286,10 +358,6 @@ func (r *Reader) Skip(n int64) error {
 			r.readHeader = true
 		}
 		chunkLen := int(r.buf[1]) | int(r.buf[2])<<8 | int(r.buf[3])<<16
-		if chunkLen > len(r.buf) {
-			r.err = ErrUnsupported
-			return r.err
-		}
 
 		// The chunk types are specified at
 		// https://github.com/google/snappy/blob/master/framing_format.txt
@@ -300,6 +368,10 @@ func (r *Reader) Skip(n int64) error {
 				r.err = ErrCorrupt
 				return r.err
 			}
+			if chunkLen > len(r.buf) {
+				r.err = ErrUnsupported
+				return r.err
+			}
 			buf := r.buf[:chunkLen]
 			if !r.readFull(buf, false) {
 				return r.err
@@ -312,7 +384,7 @@ func (r *Reader) Skip(n int64) error {
 				r.err = err
 				return r.err
 			}
-			if dLen > maxBlockSize {
+			if dLen > r.maxBlock {
 				r.err = ErrCorrupt
 				return r.err
 			}
@@ -342,6 +414,10 @@ func (r *Reader) Skip(n int64) error {
 				r.err = ErrCorrupt
 				return r.err
 			}
+			if chunkLen > len(r.buf) {
+				r.err = ErrUnsupported
+				return r.err
+			}
 			buf := r.buf[:checksumSize]
 			if !r.readFull(buf, false) {
 				return r.err
@@ -350,7 +426,7 @@ func (r *Reader) Skip(n int64) error {
 			// Read directly into r.decoded instead of via r.buf.
 			n2 := chunkLen - checksumSize
 			if n2 > len(r.decoded) {
-				if n2 > maxBlockSize {
+				if n2 > r.maxBlock {
 					r.err = ErrCorrupt
 					return r.err
 				}
@@ -391,13 +467,15 @@ func (r *Reader) Skip(n int64) error {
 			r.err = ErrUnsupported
 			return r.err
 		}
+		if chunkLen > maxBlockSize {
+			r.err = ErrUnsupported
+			return r.err
+		}
 		// Section 4.4 Padding (chunk type 0xfe).
 		// Section 4.6. Reserved skippable chunks (chunk types 0x80-0xfd).
-		if !r.readFull(r.buf[:chunkLen], false) {
+		if !r.skipN(r.buf, chunkLen, false) {
 			return r.err
 		}
-
-		return io.ErrUnexpectedEOF
 	}
 	return nil
 }
diff --git a/s2/decode_test.go b/s2/decode_test.go
index 0a6a8125d4..bc22c6baf0 100644
--- a/s2/decode_test.go
+++ b/s2/decode_test.go
@@ -6,6 +6,7 @@ package s2
 
 import (
 	"bytes"
+	"fmt"
 	"io/ioutil"
 	"strings"
 	"testing"
@@ -41,3 +42,120 @@ func TestDecodeRegression(t *testing.T) {
 		})
 	}
 }
+
+func TestDecoderMaxBlockSize(t *testing.T) {
+	data, err := ioutil.ReadFile("testdata/enc_regressions.zip")
+	if err != nil {
+		t.Fatal(err)
+	}
+	zr, err := zip.NewReader(bytes.NewReader(data), int64(len(data)))
+	if err != nil {
+		t.Fatal(err)
+	}
+	sizes := []int{4 << 10, 10 << 10, 1 << 20, 4 << 20}
+	test := func(t *testing.T, data []byte) {
+		for _, size := range sizes {
+			t.Run(fmt.Sprintf("%d", size), func(t *testing.T) {
+				var buf bytes.Buffer
+				dec := NewReader(nil, ReaderMaxBlockSize(size))
+				enc := NewWriter(&buf, WriterBlockSize(size), WriterPadding(16<<10), WriterPaddingSrc(zeroReader{}))
+
+				// Test writer.
+				n, err := enc.Write(data)
+				if err != nil {
+					t.Error(err)
+					return
+				}
+				if n != len(data) {
+					t.Error(fmt.Errorf("Write: Short write, want %d, got %d", len(data), n))
+					return
+				}
+				err = enc.Close()
+				if err != nil {
+					t.Error(err)
+					return
+				}
+				// Calling close twice should not affect anything.
+				err = enc.Close()
+				if err != nil {
+					t.Error(err)
+					return
+				}
+
+				dec.Reset(&buf)
+				got, err := ioutil.ReadAll(dec)
+				if err != nil {
+					t.Error(err)
+					return
+				}
+				if !bytes.Equal(data, got) {
+					t.Error("block (reset) decoder mismatch")
+					return
+				}
+
+				// Test Reset on both and use ReadFrom instead.
+				buf.Reset()
+				enc.Reset(&buf)
+				n2, err := enc.ReadFrom(bytes.NewBuffer(data))
+				if err != nil {
+					t.Error(err)
+					return
+				}
+				if n2 != int64(len(data)) {
+					t.Error(fmt.Errorf("ReadFrom: Short read, want %d, got %d", len(data), n2))
+					return
+				}
+				// Encode twice...
+				n2, err = enc.ReadFrom(bytes.NewBuffer(data))
+				if err != nil {
+					t.Error(err)
+					return
+				}
+				if n2 != int64(len(data)) {
+					t.Error(fmt.Errorf("ReadFrom: Short read, want %d, got %d", len(data), n2))
+					return
+				}
+
+				err = enc.Close()
+				if err != nil {
+					t.Error(err)
+					return
+				}
+				if enc.pad > 0 && buf.Len()%enc.pad != 0 {
+					t.Error(fmt.Errorf("wanted size to be mutiple of %d, got size %d with remainder %d", enc.pad, buf.Len(), buf.Len()%enc.pad))
+					return
+				}
+				dec.Reset(&buf)
+				// Skip first...
+				dec.Skip(int64(len(data)))
+				got, err = ioutil.ReadAll(dec)
+				if err != nil {
+					t.Error(err)
+					return
+				}
+				if !bytes.Equal(data, got) {
+					t.Error("frame (reset) decoder mismatch")
+					return
+				}
+			})
+		}
+	}
+	for _, tt := range zr.File {
+		if !strings.HasSuffix(t.Name(), "") {
+			continue
+		}
+		t.Run(tt.Name, func(t *testing.T) {
+			r, err := tt.Open()
+			if err != nil {
+				t.Error(err)
+				return
+			}
+			b, err := ioutil.ReadAll(r)
+			if err != nil {
+				t.Error(err)
+				return
+			}
+			test(t, b[:len(b):len(b)])
+		})
+	}
+}
diff --git a/s2/encode.go b/s2/encode.go
index 325e27cd3e..8f89e21a2f 100644
--- a/s2/encode.go
+++ b/s2/encode.go
@@ -983,7 +983,7 @@ func WriterUncompressed() WriterOption {
 // Default block size is 1MB.
 func WriterBlockSize(n int) WriterOption {
 	return func(w *Writer) error {
-		if w.blockSize > maxBlockSize || w.blockSize < minBlockSize {
+		if n > maxBlockSize || n < minBlockSize {
 			return errors.New("s2: block size too large. Must be <= 4MB and >=4KB")
 		}
 		w.blockSize = n
diff --git a/s2/encode_test.go b/s2/encode_test.go
index 2368d4f63b..fd668c86a3 100644
--- a/s2/encode_test.go
+++ b/s2/encode_test.go
@@ -40,7 +40,7 @@ func testOptions(t testing.TB) map[string][]WriterOption {
 	for name, opt := range testOptions {
 		x[name] = opt
 		if !testing.Short() {
-			x[name+"-1k-win"] = cloneAdd(opt, WriterBlockSize(1<<10))
+			x[name+"-4k-win"] = cloneAdd(opt, WriterBlockSize(4<<10))
 			x[name+"-4M-win"] = cloneAdd(opt, WriterBlockSize(4<<20))
 		}
 	}
@@ -80,8 +80,9 @@ func TestEncoderRegression(t *testing.T) {
 	test := func(t *testing.T, data []byte) {
 		for name, opts := range testOptions(t) {
 			t.Run(name, func(t *testing.T) {
+				var buf bytes.Buffer
 				dec := NewReader(nil)
-				enc := NewWriter(nil, opts...)
+				enc := NewWriter(&buf, opts...)
 
 				comp := Encode(make([]byte, MaxEncodedLen(len(data))), data)
 				decoded, err := Decode(nil, comp)
@@ -113,8 +114,6 @@ func TestEncoderRegression(t *testing.T) {
 				}
 
 				// Test writer.
-				var buf bytes.Buffer
-				enc.Reset(&buf)
 				n, err := enc.Write(data)
 				if err != nil {
 					t.Error(err)
@@ -152,10 +151,9 @@ func TestEncoderRegression(t *testing.T) {
 				}
 
 				// Test Reset on both and use ReadFrom instead.
-				input := bytes.NewBuffer(data)
-				buf = bytes.Buffer{}
+				buf.Reset()
 				enc.Reset(&buf)
-				n2, err := enc.ReadFrom(input)
+				n2, err := enc.ReadFrom(bytes.NewBuffer(data))
 				if err != nil {
 					t.Error(err)
 					return