diff --git a/spec/Section 3 -- Type System.md b/spec/Section 3 -- Type System.md
index d32b08566..9d353a170 100644
--- a/spec/Section 3 -- Type System.md	
+++ b/spec/Section 3 -- Type System.md	
@@ -1548,8 +1548,9 @@ Fields may accept arguments to configure their behavior. These inputs are often
 scalars or enums, but they sometimes need to represent more complex values.
 
 A GraphQL Input Object defines a set of input fields; the input fields are
-either scalars, enums, or other input objects. This allows arguments to accept
-arbitrarily complex structs.
+scalars, enums, other input objects, or any wrapping type whose underlying base
+type is one of those three. This allows arguments to accept arbitrarily complex
+structs.
 
 In this example, an Input Object called `Point2D` describes `x` and `y` inputs: