diff --git a/internal/bloomring.go b/internal/bloomring.go
index 7a603a40..c89a4e92 100644
--- a/internal/bloomring.go
+++ b/internal/bloomring.go
@@ -41,6 +41,9 @@ func NewBloomRing(slot, capacity int, falsePositiveRate float64) *BloomRing {
 }
 
 func (r *BloomRing) Add(b []byte) {
+	if r == nil {
+		return
+	}
 	r.mutex.Lock()
 	defer r.mutex.Unlock()
 	slot := r.slots[r.slotPosition]
@@ -56,6 +59,9 @@ func (r *BloomRing) Add(b []byte) {
 }
 
 func (r *BloomRing) Test(b []byte) bool {
+	if r == nil {
+		return false
+	}
 	r.mutex.RLock()
 	defer r.mutex.RUnlock()
 	for _, s := range r.slots {
diff --git a/internal/bloomring_test.go b/internal/bloomring_test.go
index 7f230215..f2d4319c 100644
--- a/internal/bloomring_test.go
+++ b/internal/bloomring_test.go
@@ -27,6 +27,16 @@ func TestBloomRing_Add(t *testing.T) {
 	bloomRingInstance.Add(make([]byte, 16))
 }
 
+func TestBloomRing_NilAdd(t *testing.T) {
+	defer func() {
+		if any := recover(); any != nil {
+			t.Fatalf("Should not got panic while adding item: %v", any)
+		}
+	}()
+	var nilRing *internal.BloomRing
+	nilRing.Add(make([]byte, 16))
+}
+
 func TestBloomRing_Test(t *testing.T) {
 	buf := []byte("shadowsocks")
 	bloomRingInstance.Add(buf)
@@ -35,6 +45,13 @@ func TestBloomRing_Test(t *testing.T) {
 	}
 }
 
+func TestBloomRing_NilTestIsFalse(t *testing.T) {
+	var nilRing *internal.BloomRing
+	if nilRing.Test([]byte("shadowsocks")) {
+		t.Fatal("Test should return false for nil BloomRing")
+	}
+}
+
 func BenchmarkBloomRing(b *testing.B) {
 	// Generate test samples with different length
 	samples := make([][]byte, internal.DefaultSFCapacity-internal.DefaultSFSlot)
diff --git a/internal/saltfilter.go b/internal/saltfilter.go
index aed9b6e0..edb7e2d1 100644
--- a/internal/saltfilter.go
+++ b/internal/saltfilter.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"os"
 	"strconv"
+	"sync"
 )
 
 // Those suggest value are all set according to
@@ -21,60 +22,60 @@ const EnvironmentPrefix = "SHADOWSOCKS_"
 // A shared instance used for checking salt repeat
 var saltfilter *BloomRing
 
-func init() {
-	var (
-		finalCapacity = DefaultSFCapacity
-		finalFPR      = DefaultSFFPR
-		finalSlot     = float64(DefaultSFSlot)
-	)
-	for _, opt := range []struct {
-		ENVName string
-		Target  *float64
-	}{
-		{
-			ENVName: "CAPACITY",
-			Target:  &finalCapacity,
-		},
-		{
-			ENVName: "FPR",
-			Target:  &finalFPR,
-		},
-		{
-			ENVName: "SLOT",
-			Target:  &finalSlot,
-		},
-	} {
-		envKey := EnvironmentPrefix + "SF_" + opt.ENVName
-		env := os.Getenv(envKey)
-		if env != "" {
-			p, err := strconv.ParseFloat(env, 64)
-			if err != nil {
-				panic(fmt.Sprintf("Invalid envrionment `%s` setting in saltfilter: %s", envKey, env))
+// Used to initialize the saltfilter singleton only once.
+var initSaltfilterOnce sync.Once
+
+// GetSaltFilterSingleton returns the BloomRing singleton,
+// initializing it on first call.
+func getSaltFilterSingleton() *BloomRing {
+	initSaltfilterOnce.Do(func() {
+		var (
+			finalCapacity = DefaultSFCapacity
+			finalFPR      = DefaultSFFPR
+			finalSlot     = float64(DefaultSFSlot)
+		)
+		for _, opt := range []struct {
+			ENVName string
+			Target  *float64
+		}{
+			{
+				ENVName: "CAPACITY",
+				Target:  &finalCapacity,
+			},
+			{
+				ENVName: "FPR",
+				Target:  &finalFPR,
+			},
+			{
+				ENVName: "SLOT",
+				Target:  &finalSlot,
+			},
+		} {
+			envKey := EnvironmentPrefix + "SF_" + opt.ENVName
+			env := os.Getenv(envKey)
+			if env != "" {
+				p, err := strconv.ParseFloat(env, 64)
+				if err != nil {
+					panic(fmt.Sprintf("Invalid envrionment `%s` setting in saltfilter: %s", envKey, env))
+				}
+				*opt.Target = p
 			}
-			*opt.Target = p
 		}
-	}
-	// Support disable saltfilter by given a negative capacity
-	if finalCapacity <= 0 {
-		return
-	}
-	saltfilter = NewBloomRing(int(finalSlot), int(finalCapacity), finalFPR)
+		// Support disable saltfilter by given a negative capacity
+		if finalCapacity <= 0 {
+			return
+		}
+		saltfilter = NewBloomRing(int(finalSlot), int(finalCapacity), finalFPR)
+	})
+	return saltfilter
 }
 
 // TestSalt returns true if salt is repeated
 func TestSalt(b []byte) bool {
-	// If nil means feature disabled, return false to bypass salt repeat detection
-	if saltfilter == nil {
-		return false
-	}
-	return saltfilter.Test(b)
+	return getSaltFilterSingleton().Test(b)
 }
 
 // AddSalt salt to filter
 func AddSalt(b []byte) {
-	// If nil means feature disabled
-	if saltfilter == nil {
-		return
-	}
-	saltfilter.Add(b)
+	getSaltFilterSingleton().Add(b)
 }