diff --git a/dogsdogsdogs/src/operators/lookup_map.rs b/dogsdogsdogs/src/operators/lookup_map.rs
index 029e1f942..a35472479 100644
--- a/dogsdogsdogs/src/operators/lookup_map.rs
+++ b/dogsdogsdogs/src/operators/lookup_map.rs
@@ -30,7 +30,7 @@ where
     G: Scope,
     G::Timestamp: Lattice,
     Tr: TraceReader<Time=G::Timestamp>+Clone+'static,
-    Tr::Key: Ord+Hashable,
+    Tr::Key: Ord+Hashable+Sized,
     Tr::Val: Clone,
     Tr::R: Monoid+ExchangeData,
     F: FnMut(&D, &mut Tr::Key)+Clone+'static,