diff --git a/src/NITTA/Intermediate/Value.hs b/src/NITTA/Intermediate/Value.hs
index 0d96aef6b..d0e369b7a 100644
--- a/src/NITTA/Intermediate/Value.hs
+++ b/src/NITTA/Intermediate/Value.hs
@@ -63,6 +63,7 @@ class
     , Bits x
     , Validity x
     , FixedPointCompatible x
+    , ToJSON x
     ) =>
     Val x
     where