diff --git a/model/group.go b/model/group.go
index 02cc7fc..ef4f153 100644
--- a/model/group.go
+++ b/model/group.go
@@ -243,7 +243,7 @@ func (g *Group) GetAttribute(name string) (value string, exists bool) {
 func ValidateInvite(invite string) (*groups.GroupInvite, error) {
 	// We prefix invites for groups with torv3
 	if strings.HasPrefix(invite, GroupInvitePrefix) {
-		data, err := base64.StdEncoding.DecodeString(invite[5:])
+		data, err := base64.StdEncoding.DecodeString(invite[len(GroupInvitePrefix):])
 		if err == nil {
 			// First attempt to unmarshal the json...
 			var gci groups.GroupInvite