diff --git a/src/lib_micheline/micheline.ml b/src/lib_micheline/micheline.ml
index 7a34d1f6548f5fd3ed902eb6b8f0d6a03873527c..85d3267458a4accf527d1f387a1d2b2b279eab35 100644
--- a/src/lib_micheline/micheline.ml
+++ b/src/lib_micheline/micheline.ml
@@ -38,7 +38,7 @@ type canonical_location = int
 
 let dummy_location = -1
 
-type 'p canonical = Canonical of (canonical_location, 'p) node
+type 'p canonical = Canonical of (canonical_location, 'p) node [@@unboxed]
 
 let location = function
   | Int (loc, _) -> loc