diff --git a/zstd/encoder_test.go b/zstd/encoder_test.go
index 41ce246094..53fe6f6437 100644
--- a/zstd/encoder_test.go
+++ b/zstd/encoder_test.go
@@ -11,7 +11,9 @@ import (
 	"io/ioutil"
 	"math/rand"
 	"os"
+	"runtime"
 	"strings"
+	"sync"
 	"testing"
 	"time"
 
@@ -57,6 +59,57 @@ func TestEncoder_EncodeAllSimple(t *testing.T) {
 	}
 }
 
+func TestEncoder_EncodeAllConcurrent(t *testing.T) {
+	in, err := ioutil.ReadFile("testdata/z000028")
+	if err != nil {
+		t.Fatal(err)
+	}
+	in = append(in, in...)
+
+	// When running race no more than 8k goroutines allowed.
+	n := 4000 / runtime.GOMAXPROCS(0)
+	if testing.Short() {
+		n = 200 / runtime.GOMAXPROCS(0)
+	}
+	dec, err := NewReader(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer dec.Close()
+	for level := EncoderLevel(speedNotSet + 1); level < speedLast; level++ {
+		t.Run(level.String(), func(t *testing.T) {
+			rng := rand.New(rand.NewSource(0x1337))
+			e, err := NewWriter(nil, WithEncoderLevel(level), WithZeroFrames(true))
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer e.Close()
+			var wg sync.WaitGroup
+			wg.Add(n)
+			for i := 0; i < n; i++ {
+				in := in[rng.Int()&1023:]
+				in = in[:rng.Intn(len(in))]
+				go func() {
+					defer wg.Done()
+					dst := e.EncodeAll(in, nil)
+					//t.Log("Simple Encoder len", len(in), "-> zstd len", len(dst))
+					decoded, err := dec.DecodeAll(dst, nil)
+					if err != nil {
+						t.Error(err, len(decoded))
+					}
+					if !bytes.Equal(decoded, in) {
+						//ioutil.WriteFile("testdata/"+t.Name()+"-z000028.got", decoded, os.ModePerm)
+						//ioutil.WriteFile("testdata/"+t.Name()+"-z000028.want", in, os.ModePerm)
+						t.Fatal("Decoded does not match")
+					}
+				}()
+			}
+			wg.Wait()
+			t.Log("Encoded content matched.", n, "goroutines")
+		})
+	}
+}
+
 func TestEncoder_EncodeAllEncodeXML(t *testing.T) {
 	f, err := os.Open("testdata/xml.zst")
 	if err != nil {
diff --git a/zstd/fse_encoder.go b/zstd/fse_encoder.go
index dfa6cf7cea..c657c3acca 100644
--- a/zstd/fse_encoder.go
+++ b/zstd/fse_encoder.go
@@ -502,6 +502,14 @@ func (s *fseEncoder) validateNorm() (err error) {
 // writeCount will write the normalized histogram count to header.
 // This is read back by readNCount.
 func (s *fseEncoder) writeCount(out []byte) ([]byte, error) {
+	if s.useRLE {
+		return append(out, s.rleVal), nil
+	}
+	if s.preDefined || s.reUsed {
+		// Never write predefined.
+		return out, nil
+	}
+
 	var (
 		tableLog  = s.actualTableLog
 		tableSize = 1 << tableLog
@@ -516,15 +524,12 @@ func (s *fseEncoder) writeCount(out []byte) ([]byte, error) {
 		remaining = int16(tableSize + 1) /* +1 for extra accuracy */
 		threshold = int16(tableSize)
 		nbBits    = uint(tableLog + 1)
+		outP      = len(out)
 	)
-	if s.useRLE {
-		return append(out, s.rleVal), nil
-	}
-	if s.preDefined || s.reUsed {
-		// Never write predefined.
-		return out, nil
+	if cap(out) < outP+maxHeaderSize {
+		out = append(out, make([]byte, maxHeaderSize*3)...)
+		out = out[:len(out)-maxHeaderSize*3]
 	}
-	outP := len(out)
 	out = out[:outP+maxHeaderSize]
 
 	// stops at 1
@@ -598,7 +603,7 @@ func (s *fseEncoder) writeCount(out []byte) ([]byte, error) {
 	out[outP+1] = byte(bitStream >> 8)
 	outP += int((bitCount + 7) / 8)
 
-	if uint16(charnum) > s.symbolLen {
+	if charnum > s.symbolLen {
 		return nil, errors.New("internal error: charnum > s.symbolLen")
 	}
 	return out[:outP], nil