diff --git a/rebar.config b/rebar.config
index 289fed3..f134a63 100644
--- a/rebar.config
+++ b/rebar.config
@@ -1,4 +1,4 @@
-{require_otp_vsn, "R14|R15|R16|17|18|19|20"}.
+{require_otp_vsn, "R14|R15|R16|17|18|19|20|21"}.
 
 {erl_opts, [debug_info, warn_unused_vars, warn_shadow_vars, warn_unused_import]}.
 {port_sources, ["c_src/*.cc",