diff --git a/lib/kernel/comby_kernel.mli b/lib/kernel/comby_kernel.mli
index 5ee74b9..4c5f7f7 100644
--- a/lib/kernel/comby_kernel.mli
+++ b/lib/kernel/comby_kernel.mli
@@ -1,3 +1,5 @@
+open Core_kernel
+
 (** {2 Match}
 
     A match is a result of matching a template pattern in an input source.