diff --git a/graph/mongo/iterator.go b/graph/mongo/iterator.go
index 9e37089..0c54910 100644
--- a/graph/mongo/iterator.go
+++ b/graph/mongo/iterator.go
@@ -185,13 +185,13 @@ func (it *Iterator) Contains(v graph.Value) bool {
 	case quad.Subject:
 		offset = 0
 	case quad.Predicate:
-		offset = (it.qs.hasher.Size() * 2)
+		offset = (it.qs.hasher_size * 2)
 	case quad.Object:
-		offset = (it.qs.hasher.Size() * 2) * 2
+		offset = (it.qs.hasher_size * 2) * 2
 	case quad.Label:
-		offset = (it.qs.hasher.Size() * 2) * 3
+		offset = (it.qs.hasher_size * 2) * 3
 	}
-	val := v.(string)[offset : it.qs.hasher.Size()*2+offset]
+	val := v.(string)[offset : it.qs.hasher_size*2+offset]
 	if val == it.hash {
 		it.result = v
 		return graph.ContainsLogOut(it, v, true)
diff --git a/graph/mongo/triplestore.go b/graph/mongo/triplestore.go
index 364d195..9df314d 100644
--- a/graph/mongo/triplestore.go
+++ b/graph/mongo/triplestore.go
@@ -39,10 +39,11 @@ var _ graph.BulkLoader = (*TripleStore)(nil)
 const DefaultDBName = "cayley"
 
 type TripleStore struct {
-	session *mgo.Session
-	db      *mgo.Database
-	hasher  hash.Hash
-	idCache *IDLru
+	session     *mgo.Session
+	db          *mgo.Database
+	hasher_size int
+	make_hasher func() hash.Hash
+	idCache     *IDLru
 }
 
 func createNewMongoGraph(addr string, options graph.Options) error {
@@ -86,24 +87,26 @@ func newTripleStore(addr string, options graph.Options) (graph.TripleStore, erro
 	}
 	qs.db = conn.DB(dbName)
 	qs.session = conn
-	qs.hasher = sha1.New()
+	qs.hasher_size = sha1.Size
+	qs.make_hasher = func() hash.Hash { return sha1.New() }
 	qs.idCache = NewIDLru(1 << 16)
 	return &qs, nil
 }
 
 func (qs *TripleStore) getIdForTriple(t quad.Quad) string {
-	id := qs.ConvertStringToByteHash(t.Subject)
-	id += qs.ConvertStringToByteHash(t.Predicate)
-	id += qs.ConvertStringToByteHash(t.Object)
-	id += qs.ConvertStringToByteHash(t.Label)
+	hasher := qs.make_hasher()
+	id := qs.convertStringToByteHash(t.Subject, hasher)
+	id += qs.convertStringToByteHash(t.Predicate, hasher)
+	id += qs.convertStringToByteHash(t.Object, hasher)
+	id += qs.convertStringToByteHash(t.Label, hasher)
 	return id
 }
 
-func (qs *TripleStore) ConvertStringToByteHash(s string) string {
-	qs.hasher.Reset()
-	key := make([]byte, 0, qs.hasher.Size())
-	qs.hasher.Write([]byte(s))
-	key = qs.hasher.Sum(key)
+func (qs *TripleStore) convertStringToByteHash(s string, hasher hash.Hash) string {
+	hasher.Reset()
+	key := make([]byte, 0, qs.hasher_size)
+	hasher.Write([]byte(s))
+	key = hasher.Sum(key)
 	return hex.EncodeToString(key)
 }
 
@@ -243,7 +246,8 @@ func (qs *TripleStore) TriplesAllIterator() graph.Iterator {
 }
 
 func (qs *TripleStore) ValueOf(s string) graph.Value {
-	return qs.ConvertStringToByteHash(s)
+	h := qs.make_hasher()
+	return qs.convertStringToByteHash(s, h)
 }
 
 func (qs *TripleStore) NameOf(v graph.Value) string {
@@ -288,13 +292,13 @@ func (qs *TripleStore) TripleDirection(in graph.Value, d quad.Direction) graph.V
 	case quad.Subject:
 		offset = 0
 	case quad.Predicate:
-		offset = (qs.hasher.Size() * 2)
+		offset = (qs.hasher_size * 2)
 	case quad.Object:
-		offset = (qs.hasher.Size() * 2) * 2
+		offset = (qs.hasher_size * 2) * 2
 	case quad.Label:
-		offset = (qs.hasher.Size() * 2) * 3
+		offset = (qs.hasher_size * 2) * 3
 	}
-	val := in.(string)[offset : qs.hasher.Size()*2+offset]
+	val := in.(string)[offset : qs.hasher_size*2+offset]
 	return val
 }