diff --git a/roaring.go b/roaring.go
index 5a2dbebd..dd8e6f19 100644
--- a/roaring.go
+++ b/roaring.go
@@ -198,7 +198,7 @@ func (rb *Bitmap) String() string {
 			buffer.WriteString("...")
 			break
 		}
-		buffer.WriteString(strconv.Itoa(int(i.Next())))
+		buffer.WriteString(strconv.FormatInt(int64(i.Next()), 10))
 		if i.HasNext() { // todo: optimize
 			buffer.WriteString(",")
 		}
diff --git a/roaring_test.go b/roaring_test.go
index 234ed355..2a862237 100644
--- a/roaring_test.go
+++ b/roaring_test.go
@@ -8,6 +8,15 @@ import (
 	"strconv"
 	"testing"
 )
+func TestStringer(t *testing.T) {
+	v := NewBitmap()
+	for i := uint32(0); i < 10; i++ {
+		v.Add(i)
+	}
+	if v.String() != "{0,1,2,3,4,5,6,7,8,9}" {
+		t.Error("bad string output")
+	}
+}
 
 func TestFastCard(t *testing.T) {
 	Convey("fast card", t, func() {