diff --git a/DTLSSocket/dtls.pyx b/DTLSSocket/dtls.pyx
index f70aa1b7f0bb8c69aff88b5aa6929aadff41c148..fb061a8a65b4871ae890d4f21fa71e373c3ccff5 100644
--- a/DTLSSocket/dtls.pyx
+++ b/DTLSSocket/dtls.pyx
@@ -1,3 +1,4 @@
+# cython: language_level=2
 cimport tdtls
 from tdtls cimport dtls_context_t, dtls_handler_t, session_t, dtls_alert_level_t, dtls_credentials_type_t
 from libc.stdint cimport uint8_t