diff --git a/src/proto_alpha/lib_protocol/src/alpha_context.mli b/src/proto_alpha/lib_protocol/src/alpha_context.mli
index 7a739c37b..87bd553ce 100644
--- a/src/proto_alpha/lib_protocol/src/alpha_context.mli
+++ b/src/proto_alpha/lib_protocol/src/alpha_context.mli
@@ -67,6 +67,7 @@ module Period : sig
   type period = t
 
   val of_seconds: int64 -> period tzresult
+  val to_seconds: period -> int64
   val mult: int32 -> period -> period tzresult
 
   val one_second: period