diff --git a/src/clj/com/rpl/specter/impl.cljx b/src/clj/com/rpl/specter/impl.cljx
index d78627d..84b592f 100644
--- a/src/clj/com/rpl/specter/impl.cljx
+++ b/src/clj/com/rpl/specter/impl.cljx
@@ -23,9 +23,17 @@
 (defprotocol PathComposer
   (comp-paths* [paths]))
 
+(defn- smart-str* [o]
+  (if (coll? o)
+    (pr-str o)
+    (str o)))
+
+(defn smart-str [& elems]
+  (apply str (map smart-str* elems)))
+
 #+clj
 (defmacro throw* [etype & args]
-  `(throw (new ~etype (pr-str ~@args))))
+  `(throw (new ~etype (smart-str ~@args))))
 
 #+clj
 (defmacro throw-illegal [& args]
diff --git a/src/clj/com/rpl/specter/macros.clj b/src/clj/com/rpl/specter/macros.clj
index b25738a..a8d5141 100644
--- a/src/clj/com/rpl/specter/macros.clj
+++ b/src/clj/com/rpl/specter/macros.clj
@@ -6,6 +6,9 @@
   (vec (repeatedly amt gensym)))
 
 (defn determine-params-impls [[name1 & impl1] [name2 & impl2]]
+  (if-not (= #{name1 name2} #{'select* 'transform*})
+    (throw-illegal "defpath must implement select* and transform*, instead got "
+      name1 " and " name2))
   (if (= name1 'select*)
     [impl1 impl2]
     [impl2 impl1]))