diff --git a/stream.go b/stream.go
index b630b78..037c22d 100644
--- a/stream.go
+++ b/stream.go
@@ -422,15 +422,9 @@ func (s *Stream) readData(hdr header, flags uint16, conn io.Reader) error {
 		return nil
 	}
 
-	// Validate it's okay to copy
-	if !s.recvBuf.TryReserve(length) {
-		s.session.logger.Printf("[ERR] yamux: receive window exceeded (stream: %d, remain: %d, recv: %d)", s.id, s.recvBuf.Cap(), length)
-		return ErrRecvWindowExceeded
-	}
-
 	// Copy into buffer
-	if err := s.recvBuf.Append(conn, int(length)); err != nil {
-		s.session.logger.Printf("[ERR] yamux: Failed to read stream data: %v", err)
+	if err := s.recvBuf.Append(conn, length); err != nil {
+		s.session.logger.Printf("[ERR] yamux: Failed to read stream data on stream %d: %v", s.id, err)
 		return err
 	}
 	// Unblock the reader
diff --git a/util.go b/util.go
index 45da28c..177eb98 100644
--- a/util.go
+++ b/util.go
@@ -1,6 +1,7 @@
 package yamux
 
 import (
+	"fmt"
 	"io"
 	"sync"
 
@@ -42,14 +43,12 @@ func min(values ...uint32) uint32 {
 //      |     data      | empty space       |
 //       < window (10)                     >
 //       < len (5)     > < cap (5)         >
-//                       < pending (4)    >
 //
 // As data is read, the buffer gets updated like so:
 //
 //         |     data   | empty space       |
 //          < window (8)                   >
 //          < len (3)  > < cap (5)         >
-//                       < pending (4)    >
 //
 // It can then grow as follows (given a "max" of 10):
 //
@@ -57,21 +56,18 @@ func min(values ...uint32) uint32 {
 //         |     data   | empty space          |
 //          < window (10)                     >
 //          < len (3)  > < cap (7)            >
-//                       < pending (4)    >
 //
-// Data can then be written into the pending space, expanding len, and shrinking
-// cap and pending:
+// Data can then be written into the empty space, expanding len,
+// and shrinking cap:
 //
 //         |     data       | empty space      |
 //          < window (10)                     >
 //          < len (5)      > < cap (5)        >
-//                           < pending (2)>
 //
 type segmentedBuffer struct {
-	cap     uint32
-	pending uint32
-	len     uint32
-	bm      sync.Mutex
+	cap uint32
+	len uint32
+	bm  sync.Mutex
 	// read position in b[0].
 	// We must not reslice any of the buffers in b, as we need to put them back into the pool.
 	readPos int
@@ -84,22 +80,10 @@ func newSegmentedBuffer(initialCapacity uint32) segmentedBuffer {
 }
 
 // Len is the amount of data in the receive buffer.
-func (s *segmentedBuffer) Len() int {
+func (s *segmentedBuffer) Len() uint32 {
 	s.bm.Lock()
-	len := s.len
-	s.bm.Unlock()
-	return int(len)
-}
-
-// Cap is the remaining capacity in the receive buffer.
-//
-// Note: this is _not_ the same as go's 'cap' function. The total size of the
-// buffer is len+cap.
-func (s *segmentedBuffer) Cap() uint32 {
-	s.bm.Lock()
-	cap := s.cap
-	s.bm.Unlock()
-	return cap
+	defer s.bm.Unlock()
+	return s.len
 }
 
 // If the space to write into + current buffer size has grown to half of the window size,
@@ -122,16 +106,6 @@ func (s *segmentedBuffer) GrowTo(max uint32, force bool) (bool, uint32) {
 	return true, delta
 }
 
-func (s *segmentedBuffer) TryReserve(space uint32) bool {
-	s.bm.Lock()
-	defer s.bm.Unlock()
-	if s.cap < s.pending+space {
-		return false
-	}
-	s.pending += space
-	return true
-}
-
 func (s *segmentedBuffer) Read(b []byte) (int, error) {
 	s.bm.Lock()
 	defer s.bm.Unlock()
@@ -154,8 +128,21 @@ func (s *segmentedBuffer) Read(b []byte) (int, error) {
 	return n, nil
 }
 
-func (s *segmentedBuffer) Append(input io.Reader, length int) error {
-	dst := pool.Get(length)
+func (s *segmentedBuffer) checkOverflow(l uint32) error {
+	s.bm.Lock()
+	defer s.bm.Unlock()
+	if s.cap < l {
+		return fmt.Errorf("receive window exceeded (remain: %d, recv: %d)", s.cap, l)
+	}
+	return nil
+}
+
+func (s *segmentedBuffer) Append(input io.Reader, length uint32) error {
+	if err := s.checkOverflow(length); err != nil {
+		return err
+	}
+
+	dst := pool.Get(int(length))
 	n, err := io.ReadFull(input, dst)
 	if err == io.EOF {
 		err = io.ErrUnexpectedEOF
@@ -165,7 +152,6 @@ func (s *segmentedBuffer) Append(input io.Reader, length int) error {
 	if n > 0 {
 		s.len += uint32(n)
 		s.cap -= uint32(n)
-		s.pending = s.pending - uint32(length)
 		s.b = append(s.b, dst[0:n])
 	}
 	return err
diff --git a/util_test.go b/util_test.go
index 68fb3ba..90b9cbe 100644
--- a/util_test.go
+++ b/util_test.go
@@ -54,18 +54,17 @@ func TestMin(t *testing.T) {
 
 func TestSegmentedBuffer(t *testing.T) {
 	buf := newSegmentedBuffer(100)
-	assert := func(len, cap int) {
+	assert := func(len, cap uint32) {
 		if buf.Len() != len {
 			t.Fatalf("expected length %d, got %d", len, buf.Len())
 		}
-		if buf.Cap() != uint32(cap) {
+		buf.bm.Lock()
+		defer buf.bm.Unlock()
+		if buf.cap != cap {
 			t.Fatalf("expected length %d, got %d", len, buf.Len())
 		}
 	}
 	assert(0, 100)
-	if !buf.TryReserve(3) {
-		t.Fatal("reservation should have worked")
-	}
 	if err := buf.Append(bytes.NewReader([]byte("fooo")), 3); err != nil {
 		t.Fatal(err)
 	}
@@ -87,9 +86,6 @@ func TestSegmentedBuffer(t *testing.T) {
 		t.Fatal("should have grown by 2")
 	}
 
-	if !buf.TryReserve(50) {
-		t.Fatal("reservation should have worked")
-	}
 	if err := buf.Append(bytes.NewReader(make([]byte, 50)), 50); err != nil {
 		t.Fatal(err)
 	}
@@ -104,9 +100,7 @@ func TestSegmentedBuffer(t *testing.T) {
 	if read != 50 {
 		t.Fatal("expected to read 50 bytes")
 	}
-	if !buf.TryReserve(49) {
-		t.Fatal("should have been able to reserve rest of space")
-	}
+
 	assert(1, 49)
 	if grew, amount := buf.GrowTo(100, false); !grew || amount != 50 {
 		t.Fatal("should have grown when below half, even with reserved space")