diff --git a/hash.go b/hash.go
index 46927a1..d05a06e 100644
--- a/hash.go
+++ b/hash.go
@@ -5,10 +5,9 @@ import (
 	"fmt"
 	"hash"
 	"io"
+	"net/http"
 	"net/mail"
 	"sort"
-
-	"github.com/golang/glog"
 )
 
 // Hasher is a list of headers that should be considered when hashing an email
@@ -17,18 +16,20 @@ type Hasher []string
 
 // Hash will parse r as an email, and return a hash.Hash that has been applied
 // to the values of the headers in h.
-func (h Hasher) HashMessage(msg *mail.Message) (hash.Hash, error) {
+func (hsr Hasher) HashMessage(msg *mail.Message) (hash.Hash, error) {
 	// Add deterministic behavior regardless of the order the users specified.
-	if !sort.IsSorted(sort.StringSlice(h)) {
-		sort.Strings(h)
+	if !sort.IsSorted(sort.StringSlice(hsr)) {
+		sort.Strings(hsr)
 	}
 	hsh := sha1.New()
-	for _, header := range h {
-		v := msg.Header.Get(header)
-		if v == "" {
-			glog.V(2).Infoln("Empty", header, "header")
+	for _, h := range hsr {
+		h := http.CanonicalHeaderKey(h)
+		vs, ok := msg.Header[h]
+		if ok {
+			for _, v := range vs {
+				io.WriteString(hsh, v)
+			}
 		}
-		io.WriteString(hsh, v)
 	}
 	return hsh, nil
 }
@@ -41,7 +42,7 @@ func (h Hasher) HashReader(r io.Reader) (hash.Hash, error) {
 	return h.HashMessage(msg)
 }
 
-var std = Hasher([]string{"to", "from", "cc", "date", "subject", "message-id"})
+var std = Hasher([]string{"to", "from", "cc", "date", "subject", "message-id", "received"})
 
 // Hash will parse r as an email, and return the hash as a hexadecimal string
 // using a default set of headers.