diff --git a/extra/size-of/size-of.factor b/extra/size-of/size-of.factor
index 06a7067636..4f4743c6b6 100644
--- a/extra/size-of/size-of.factor
+++ b/extra/size-of/size-of.factor
@@ -12,6 +12,8 @@ DEFER: size-of
 
 HELP: size-of
 
+Values: HEADERS sequence  TYPE string  n integer ..
+
 Description:
 
     Use 'size-of' to find out the size in bytes of a C type.