diff --git a/compress_generate.go b/compress_generate.go
index 9a136c41..4bcefcb8 100644
--- a/compress_generate.go
+++ b/compress_generate.go
@@ -101,7 +101,7 @@ Names:
 
 	// compressionLenHelperType - all types that have domain-name/cdomain-name can be used for compressing names
 
-	fmt.Fprint(b, "func compressionLenHelperType(c map[string]int, r RR, initLen int) int {\n")
+	fmt.Fprint(b, "func compressionLenHelperType(c map[string]struct{}, r RR, initLen int) int {\n")
 	fmt.Fprint(b, "currentLen := initLen\n")
 	fmt.Fprint(b, "switch x := r.(type) {\n")
 	for _, name := range domainTypes {
@@ -145,7 +145,7 @@ Names:
 
 	// compressionLenSearchType - search cdomain-tags types for compressible names.
 
-	fmt.Fprint(b, "func compressionLenSearchType(c map[string]int, r RR) (int, bool, int) {\n")
+	fmt.Fprint(b, "func compressionLenSearchType(c map[string]struct{}, r RR) (int, bool, int) {\n")
 	fmt.Fprint(b, "switch x := r.(type) {\n")
 	for _, name := range cdomainTypes {
 		o := scope.Lookup(name)
diff --git a/dns_bench_test.go b/dns_bench_test.go
index 3fdfc03f..8653f8ff 100644
--- a/dns_bench_test.go
+++ b/dns_bench_test.go
@@ -1,6 +1,7 @@
 package dns
 
 import (
+	"fmt"
 	"net"
 	"testing"
 )
@@ -63,6 +64,31 @@ func BenchmarkMsgLengthPack(b *testing.B) {
 	}
 }
 
+func BenchmarkMsgLengthMassive(b *testing.B) {
+	makeMsg := func(question string, ans, ns, e []RR) *Msg {
+		msg := new(Msg)
+		msg.SetQuestion(Fqdn(question), TypeANY)
+		msg.Answer = append(msg.Answer, ans...)
+		msg.Ns = append(msg.Ns, ns...)
+		msg.Extra = append(msg.Extra, e...)
+		msg.Compress = true
+		return msg
+	}
+	const name1 = "12345678901234567890123456789012345.12345678.123."
+	rrMx := testRR(name1 + " 3600 IN MX 10 " + name1)
+	answer := []RR{rrMx, rrMx}
+	for i := 0; i < 128; i++ {
+		rrA := testRR(fmt.Sprintf("example%03d.something%03delse.org. 2311 IN A 127.0.0.1", i/32, i%32))
+		answer = append(answer, rrA)
+	}
+	answer = append(answer, rrMx, rrMx)
+	msg := makeMsg(name1, answer, nil, nil)
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		msg.Len()
+	}
+}
+
 func BenchmarkMsgLengthOnlyQuestion(b *testing.B) {
 	msg := new(Msg)
 	msg.SetQuestion(Fqdn("12345678901234567890123456789012345.12345678.123."), TypeANY)
diff --git a/length_test.go b/length_test.go
index cb16741d..17bca197 100644
--- a/length_test.go
+++ b/length_test.go
@@ -4,7 +4,6 @@ import (
 	"encoding/hex"
 	"fmt"
 	"net"
-	"reflect"
 	"strings"
 	"testing"
 )
@@ -83,85 +82,85 @@ func TestMsgLength(t *testing.T) {
 }
 
 func TestCompressionLenHelper(t *testing.T) {
-	c := make(map[string]int)
+	c := make(map[string]struct{})
 	compressionLenHelper(c, "example.com", 12)
-	if c["example.com"] != 12 {
-		t.Errorf("bad %d", c["example.com"])
+	if _, ok := c["example.com"]; !ok {
+		t.Errorf("bad example.com")
 	}
-	if c["com"] != 20 {
-		t.Errorf("bad %d", c["com"])
+	if _, ok := c["com"]; !ok {
+		t.Errorf("bad com")
 	}
 
 	// Test boundaries
-	c = make(map[string]int)
+	c = make(map[string]struct{})
 	// foo label starts at 16379
 	// com label starts at 16384
 	compressionLenHelper(c, "foo.com", 16379)
-	if c["foo.com"] != 16379 {
-		t.Errorf("bad %d", c["foo.com"])
+	if _, ok := c["foo.com"]; !ok {
+		t.Errorf("bad foo.com")
 	}
 	// com label is accessible
-	if c["com"] != 16383 {
-		t.Errorf("bad %d", c["com"])
+	if _, ok := c["com"]; !ok {
+		t.Errorf("bad com")
 	}
 
-	c = make(map[string]int)
+	c = make(map[string]struct{})
 	// foo label starts at 16379
 	// com label starts at 16385 => outside range
 	compressionLenHelper(c, "foo.com", 16380)
-	if c["foo.com"] != 16380 {
-		t.Errorf("bad %d", c["foo.com"])
+	if _, ok := c["foo.com"]; !ok {
+		t.Errorf("bad foo.com")
 	}
 	// com label is NOT accessible
-	if c["com"] != 0 {
-		t.Errorf("bad %d", c["com"])
+	if _, ok := c["com"]; ok {
+		t.Errorf("bad com")
 	}
 
-	c = make(map[string]int)
+	c = make(map[string]struct{})
 	compressionLenHelper(c, "example.com", 16375)
-	if c["example.com"] != 16375 {
-		t.Errorf("bad %d", c["example.com"])
+	if _, ok := c["example.com"]; !ok {
+		t.Errorf("bad example.com")
 	}
 	// com starts AFTER 16384
-	if c["com"] != 16383 {
-		t.Errorf("bad %d", c["com"])
+	if _, ok := c["com"]; !ok {
+		t.Errorf("bad com")
 	}
 
-	c = make(map[string]int)
+	c = make(map[string]struct{})
 	compressionLenHelper(c, "example.com", 16376)
-	if c["example.com"] != 16376 {
-		t.Errorf("bad %d", c["example.com"])
+	if _, ok := c["example.com"]; !ok {
+		t.Errorf("bad example.com")
 	}
 	// com starts AFTER 16384
-	if c["com"] != 0 {
-		t.Errorf("bad %d", c["com"])
+	if _, ok := c["com"]; ok {
+		t.Errorf("bad com")
 	}
 }
 
 func TestCompressionLenSearch(t *testing.T) {
-	c := make(map[string]int)
+	c := make(map[string]struct{})
 	compressed, ok, fullSize := compressionLenSearch(c, "a.b.org.")
 	if compressed != 0 || ok || fullSize != 14 {
 		t.Errorf("Failed: compressed:=%d, ok:=%v, fullSize:=%d", compressed, ok, fullSize)
 	}
-	c["org."] = 3
+	c["org."] = struct{}{}
 	compressed, ok, fullSize = compressionLenSearch(c, "a.b.org.")
 	if compressed != 4 || !ok || fullSize != 8 {
 		t.Errorf("Failed: compressed:=%d, ok:=%v, fullSize:=%d", compressed, ok, fullSize)
 	}
-	c["b.org."] = 5
+	c["b.org."] = struct{}{}
 	compressed, ok, fullSize = compressionLenSearch(c, "a.b.org.")
 	if compressed != 6 || !ok || fullSize != 4 {
 		t.Errorf("Failed: compressed:=%d, ok:=%v, fullSize:=%d", compressed, ok, fullSize)
 	}
 	// Not found long compression
-	c["x.b.org."] = 5
+	c["x.b.org."] = struct{}{}
 	compressed, ok, fullSize = compressionLenSearch(c, "a.b.org.")
 	if compressed != 6 || !ok || fullSize != 4 {
 		t.Errorf("Failed: compressed:=%d, ok:=%v, fullSize:=%d", compressed, ok, fullSize)
 	}
 	// Found long compression
-	c["a.b.org."] = 5
+	c["a.b.org."] = struct{}{}
 	compressed, ok, fullSize = compressionLenSearch(c, "a.b.org.")
 	if compressed != 8 || !ok || fullSize != 0 {
 		t.Errorf("Failed: compressed:=%d, ok:=%v, fullSize:=%d", compressed, ok, fullSize)
@@ -262,6 +261,20 @@ func TestMsgCompressLengthLargeRecords(t *testing.T) {
 	}
 }
 
+func compressionMapsEqual(a map[string]struct{}, b map[string]int) bool {
+	if len(a) != len(b) {
+		return false
+	}
+
+	for k := range a {
+		if _, ok := b[k]; !ok {
+			return false
+		}
+	}
+
+	return true
+}
+
 func TestCompareCompressionMapsForANY(t *testing.T) {
 	msg := new(Msg)
 	msg.Compress = true
@@ -278,7 +291,7 @@ func TestCompareCompressionMapsForANY(t *testing.T) {
 	for labelSize := 0; labelSize < 63; labelSize++ {
 		msg.SetQuestion(fmt.Sprintf("a%s.service.acme.", strings.Repeat("x", labelSize)), TypeANY)
 
-		compressionFake := make(map[string]int)
+		compressionFake := make(map[string]struct{})
 		lenFake := compressedLenWithCompressionMap(msg, compressionFake)
 
 		compressionReal := make(map[string]int)
@@ -289,7 +302,7 @@ func TestCompareCompressionMapsForANY(t *testing.T) {
 		if lenFake != len(buf) {
 			t.Fatalf("padding= %d ; Predicted len := %d != real:= %d", labelSize, lenFake, len(buf))
 		}
-		if !reflect.DeepEqual(compressionFake, compressionReal) {
+		if !compressionMapsEqual(compressionFake, compressionReal) {
 			t.Fatalf("padding= %d ; Fake Compression Map != Real Compression Map\n*** Real:= %v\n\n***Fake:= %v", labelSize, compressionReal, compressionFake)
 		}
 	}
@@ -311,7 +324,7 @@ func TestCompareCompressionMapsForSRV(t *testing.T) {
 	for labelSize := 0; labelSize < 63; labelSize++ {
 		msg.SetQuestion(fmt.Sprintf("a%s.service.acme.", strings.Repeat("x", labelSize)), TypeAAAA)
 
-		compressionFake := make(map[string]int)
+		compressionFake := make(map[string]struct{})
 		lenFake := compressedLenWithCompressionMap(msg, compressionFake)
 
 		compressionReal := make(map[string]int)
@@ -322,7 +335,7 @@ func TestCompareCompressionMapsForSRV(t *testing.T) {
 		if lenFake != len(buf) {
 			t.Fatalf("padding= %d ; Predicted len := %d != real:= %d", labelSize, lenFake, len(buf))
 		}
-		if !reflect.DeepEqual(compressionFake, compressionReal) {
+		if !compressionMapsEqual(compressionFake, compressionReal) {
 			t.Fatalf("padding= %d ; Fake Compression Map != Real Compression Map\n*** Real:= %v\n\n***Fake:= %v", labelSize, compressionReal, compressionFake)
 		}
 	}
diff --git a/msg.go b/msg.go
index 4208eb45..90f02973 100644
--- a/msg.go
+++ b/msg.go
@@ -907,7 +907,7 @@ func (dns *Msg) isCompressible() bool {
 		len(dns.Ns) > 0 || len(dns.Extra) > 0
 }
 
-func compressedLenWithCompressionMap(dns *Msg, compression map[string]int) int {
+func compressedLenWithCompressionMap(dns *Msg, compression map[string]struct{}) int {
 	l := 12 // Message header is always 12 bytes
 	for _, r := range dns.Question {
 		compressionLenHelper(compression, r.Name, l)
@@ -927,7 +927,7 @@ func compressedLen(dns *Msg, compress bool) int {
 	// If this message can't be compressed, avoid filling the
 	// compression map and creating garbage.
 	if compress && dns.isCompressible() {
-		compression := map[string]int{}
+		compression := make(map[string]struct{})
 		return compressedLenWithCompressionMap(dns, compression)
 	}
 
@@ -954,7 +954,7 @@ func compressedLen(dns *Msg, compress bool) int {
 	return l
 }
 
-func compressionLenSlice(lenp int, c map[string]int, rs []RR) int {
+func compressionLenSlice(lenp int, c map[string]struct{}, rs []RR) int {
 	initLen := lenp
 	for _, r := range rs {
 		if r == nil {
@@ -986,7 +986,7 @@ func compressionLenSlice(lenp int, c map[string]int, rs []RR) int {
 }
 
 // Put the parts of the name in the compression map, return the size in bytes added in payload
-func compressionLenHelper(c map[string]int, s string, currentLen int) int {
+func compressionLenHelper(c map[string]struct{}, s string, currentLen int) int {
 	if currentLen > maxCompressionOffset {
 		// We won't be able to add any label that could be re-used later anyway
 		return 0
@@ -1005,7 +1005,7 @@ func compressionLenHelper(c map[string]int, s string, currentLen int) int {
 		if _, ok := c[pref]; !ok {
 			// If first byte label is within the first 14bits, it might be re-used later
 			if currentLen < maxCompressionOffset {
-				c[pref] = currentLen
+				c[pref] = struct{}{}
 			}
 		} else {
 			added := currentLen - initLen
@@ -1023,7 +1023,7 @@ func compressionLenHelper(c map[string]int, s string, currentLen int) int {
 // keep on searching so we get the longest match.
 // Will return the size of compression found, whether a match has been
 // found and the size of record if added in payload
-func compressionLenSearch(c map[string]int, s string) (int, bool, int) {
+func compressionLenSearch(c map[string]struct{}, s string) (int, bool, int) {
 	off := 0
 	end := false
 	if s == "" { // don't bork on bogus data
diff --git a/zcompress.go b/zcompress.go
index 6391a350..fefdd2a0 100644
--- a/zcompress.go
+++ b/zcompress.go
@@ -2,7 +2,7 @@
 
 package dns
 
-func compressionLenHelperType(c map[string]int, r RR, initLen int) int {
+func compressionLenHelperType(c map[string]struct{}, r RR, initLen int) int {
 	currentLen := initLen
 	switch x := r.(type) {
 	case *AFSDB:
@@ -107,7 +107,7 @@ func compressionLenHelperType(c map[string]int, r RR, initLen int) int {
 	return currentLen - initLen
 }
 
-func compressionLenSearchType(c map[string]int, r RR) (int, bool, int) {
+func compressionLenSearchType(c map[string]struct{}, r RR) (int, bool, int) {
 	switch x := r.(type) {
 	case *CNAME:
 		k1, ok1, sz1 := compressionLenSearch(c, x.Target)