cl-adams/adams

diff --git a/core/spec.lisp b/core/spec.lisp
index f3fa3a8..577f291 100644
--- a/core/spec.lisp
+++ b/core/spec.lisp
@@ -30,7 +30,9 @@
 (defmethod (setf specified-property) (value
 				      (res resource)
 				      (property symbol))
-  (setf (get-property property (specified-properties res)) value))
+  (let ((p (specified-properties res)))
+    (setf (get-property property p) value)
+    (setf (specified-properties res) p)))
 
 ;;  Parse specifications