diff --git a/elfeed-export.el b/elfeed-export.el
index 1d5dcbc..cd31884 100644
--- a/elfeed-export.el
+++ b/elfeed-export.el
@@ -51,7 +51,7 @@
   "Which fields to export per entry and a function to obtain the value.
 
 The function takes an entry argument for extracting the desired value."
-  :type 'alist
+  :type '(alist :key-type symbol :value-type function)
   :group 'elfeed-export)
 
 (defcustom elfeed-export-predicates