diff --git a/spec/Section 4 -- Introspection.md b/spec/Section 4 -- Introspection.md
index b260559cb..8684925a5 100644
--- a/spec/Section 4 -- Introspection.md	
+++ b/spec/Section 4 -- Introspection.md	
@@ -138,15 +138,15 @@ type __Type {
   name: String
   description: String
   # must be non-null for OBJECT and INTERFACE, otherwise null.
-  fields(includeDeprecated: Boolean = false): [__Field!]
+  fields(includeDeprecated: Boolean! = false): [__Field!]
   # must be non-null for OBJECT and INTERFACE, otherwise null.
   interfaces: [__Type!]
   # must be non-null for INTERFACE and UNION, otherwise null.
   possibleTypes: [__Type!]
   # must be non-null for ENUM, otherwise null.
-  enumValues(includeDeprecated: Boolean = false): [__EnumValue!]
+  enumValues(includeDeprecated: Boolean! = false): [__EnumValue!]
   # must be non-null for INPUT_OBJECT, otherwise null.
-  inputFields(includeDeprecated: Boolean = false): [__InputValue!]
+  inputFields(includeDeprecated: Boolean! = false): [__InputValue!]
   # must be non-null for NON_NULL and LIST, otherwise null.
   ofType: __Type
   # may be non-null for custom SCALAR, otherwise null.
@@ -167,7 +167,7 @@ enum __TypeKind {
 type __Field {
   name: String!
   description: String
-  args(includeDeprecated: Boolean = false): [__InputValue!]!
+  args(includeDeprecated: Boolean! = false): [__InputValue!]!
   type: __Type!
   isDeprecated: Boolean!
   deprecationReason: String
@@ -193,7 +193,7 @@ type __Directive {
   name: String!
   description: String
   locations: [__DirectiveLocation!]!
-  args(includeDeprecated: Boolean = false): [__InputValue!]!
+  args(includeDeprecated: Boolean! = false): [__InputValue!]!
   isRepeatable: Boolean!
 }