diff --git a/dns_test.go b/dns_test.go
index f91b4597..3ad8a894 100644
--- a/dns_test.go
+++ b/dns_test.go
@@ -316,7 +316,7 @@ func TestMsgLength2(t *testing.T) {
 	}
 }
 
-func testMsgLengthCompressionMalformed(t *testing.T) {
+func TestMsgLengthCompressionMalformed(t *testing.T) {
 	// SOA with empty hostmaster, which is illegal
 	soa := &SOA{Hdr: RR_Header{Name: ".", Rrtype: TypeSOA, Class: ClassINET, Ttl: 12345},
         Ns:      ".",
@@ -329,7 +329,7 @@ func testMsgLengthCompressionMalformed(t *testing.T) {
 	m := new(Msg)
 	m.Compress = true
 	m.Ns = []RR{soa}
-	m.Len()
+	m.Len() // Should not crash.
 }
 
 func BenchmarkMsgLength(b *testing.B) {
diff --git a/msg.go b/msg.go
index 6a7755c6..cab1842d 100644
--- a/msg.go
+++ b/msg.go
@@ -1702,6 +1702,9 @@ func compressionLenHelper(c map[string]int, s string) {
 func compressionLenSearch(c map[string]int, s string) (int, bool) {
 	off := 0
 	end := false
+	if s == "" { // don't bork on bogus data
+		return 0, false
+	}
 	for {
 		if _, ok := c[s[off:]]; ok {
 			return len(s[off:]), true