1 files changed, 1 insertions, 0 deletions
diff --git a/err.go b/err.go
index 44576ed..859c567 100644
--- a/err.go
+++ b/err.go
@@ -45,4 +45,5 @@ var (
 	errContextCancelled           = errors.New("context cancelled")
 	errCannotReceiveMessage       = errors.New("cannot receive message")
 	errNoSuchCourse               = errors.New("no such course")
+	errInvalidState               = errors.New("invalid state")
 )