diff --git a/semantic-tags/src/Tags/Taggable/Precise.hs b/semantic-tags/src/Tags/Taggable/Precise.hs
index 9fdca6d64..d11f5925b 100644
--- a/semantic-tags/src/Tags/Taggable/Precise.hs
+++ b/semantic-tags/src/Tags/Taggable/Precise.hs
@@ -187,3 +187,8 @@ class GSum t where
 instance GSum f => GSum (M1 i c f) where
   type Members (M1 i c f) = Members f
   gmembers = gmembers . unM1
+
+instance (GSum f, GSum g) => GSum (f :+: g) where
+  type Members (f :+: g) = Members f :+: Members g
+  gmembers (L1 l) = L1 (gmembers l)
+  gmembers (R1 r) = R1 (gmembers r)