diff --git a/spec/Section 4 -- Introspection.md b/spec/Section 4 -- Introspection.md
index 889db030e..853da694e 100644
--- a/spec/Section 4 -- Introspection.md	
+++ b/spec/Section 4 -- Introspection.md	
@@ -98,6 +98,8 @@ identify which actual type of the possible types has been returned.
 
 This field is implicit and does not appear in the fields list in any defined type.
 
+Note: `__typename` may not be included as a root field in a subscription
+operation.
 
 ## Schema Introspection
 
diff --git a/spec/Section 5 -- Validation.md b/spec/Section 5 -- Validation.md
index b855de085..285f72073 100644
--- a/spec/Section 5 -- Validation.md	
+++ b/spec/Section 5 -- Validation.md	
@@ -249,7 +249,8 @@ query getName {
 * Let {variableValues} be the empty set.
 * Let {groupedFieldSet} be the result of
   {CollectFields(subscriptionType, selectionSet, variableValues)}.
-* {groupedFieldSet} must have exactly one entry.
+* {groupedFieldSet} must have exactly one entry, which must not be an 
+  introspection field.
 
 **Explanatory Text**
 
@@ -305,14 +306,11 @@ fragment multipleSubscriptions on Subscription {
 }
 ```
 
-Introspection fields are counted. The following example is also invalid:
+The root field of a subscription operation must not be an introspection field.
+The following example is also invalid:
 
 ```graphql counter-example
 subscription sub {
-  newMessage {
-    body
-    sender
-  }
   __typename
 }
 ```