diff --git a/gouid.go b/gouid.go
index dad955d..85c2ff1 100644
--- a/gouid.go
+++ b/gouid.go
@@ -20,15 +20,16 @@ var (
 	MixedCaseAlpha    = []byte("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
 )
 
-// String returns a string with the given size. Ids are
-// made with cryptographically secure random bytes and
-// umatch /^[a-z0-9]$/.
+// String returns a string with the given size made up of
+// characters from the given charset. Ids are made with
+// cryptographically secure random bytes. The length of
+// charset must not exceed 256.
 func String(size int, charset []byte) string {
-	b := make([]byte, size, size)
+	b := make([]byte, size)
 	rand.Read(b)
 	for i := 0; i < size; i++ {
-		charCnt := byte(len(charset))
-		index := (b[i] / (255 / charCnt)) % charCnt
+		charCnt := len(charset)
+		index := (b[i] / byte(256/charCnt)) % byte(charCnt)
 		b[i] = charset[index]
 	}
 	return *(*string)(unsafe.Pointer(&b))
@@ -36,7 +37,7 @@ func String(size int, charset []byte) string {
 
 // Bytes returns cryptographically secure random bytes.
 func Bytes(size int) GOUID {
-	b := make([]byte, size, size)
+	b := make([]byte, size)
 	rand.Read(b)
 	return b
 }
diff --git a/gouid_test.go b/gouid_test.go
index abb92dc..24e2956 100644
--- a/gouid_test.go
+++ b/gouid_test.go
@@ -69,7 +69,7 @@ func TestBytes(t *testing.T) {
 	if len(id) != length {
 		t.Error("lengh of id was not 16")
 	}
-	if bytes.Compare(id, gouid.Bytes(length)) == 0 {
+	if bytes.Equal(id, gouid.Bytes(length)) {
 		t.Error("collision")
 	}
 }
@@ -96,7 +96,7 @@ func TestBytesUnmarshal(t *testing.T) {
 		t.Error(err)
 		t.FailNow()
 	}
-	if bytes.Compare(m["id"], []byte{1}) != 0 {
+	if !bytes.Equal(m["id"], []byte{1}) {
 		t.Errorf("bad json unmarshal: %v != %v", m["id"], []byte{1})
 	}
 }