diff --git a/ConflictSet.cpp b/ConflictSet.cpp
index fbae0e0..a94e43d 100644
--- a/ConflictSet.cpp
+++ b/ConflictSet.cpp
@@ -1944,6 +1944,8 @@ protected:
   // index into children array of particular leaf type
   int index;
 };
+// We want it to be cheap to copy
+static_assert(sizeof(IteratorBase) <= 16);
 
 struct IteratorBase::ChildAndMaxVersion {
   IteratorBase child;