diff --git a/src/built_ins.cpp b/src/built_ins.cpp
index 75bcceb..19d753e 100644
--- a/src/built_ins.cpp
+++ b/src/built_ins.cpp
@@ -302,6 +302,7 @@ namespace Slime {
             Lisp_Object* thing_cons = form;
             form = form->value.pair.rest;
             Lisp_Object_Type type = definee->type;
+            debug_break();
             switch (type) {
             case Lisp_Object_Type::Symbol: {
                 if (form != Memory::nil) {