diff --git a/ast/spec.md b/ast/spec.md
index 0ff1c87c51..07c6a6482d 100644
--- a/ast/spec.md
+++ b/ast/spec.md
@@ -144,13 +144,13 @@ interface Position {
 ### Babylon 7
 
 Flow: Node renamed from `ExistentialTypeParam` to `ExistsTypeAnnotation` [#322](https://github.com/babel/babylon/pull/322)
-  
+
 Flow: Node renamed from `NumericLiteralTypeAnnotation` to `NumberLiteralTypeAnnotation` [babel/babylon#332](https://github.com/babel/babylon/pull/332)
-  
+
 Flow: Node `Variance` which replaces the string value of the `variance` field on several nodes [babel/babylon#333](https://github.com/babel/babylon/pull/333)
 
 Flow: `ObjectTypeIndexer` location info matches Flow's better [babel/babylon#228](https://github.com/babel/babylon/pull/228)
-  
+
 Node `ForAwaitStatement` has been removed [#349](https://github.com/babel/babylon/pull/349) in favor of modifying `ForOfStatement`
 
 `RestProperty` and `SpreadProperty` have been dropped in favor of `RestElement` and `SpreadElement`.
@@ -514,7 +514,7 @@ interface FunctionDeclaration <: Function, Declaration {
 }
 ```
 
-A function declaration. Note that unlike in the parent interface `Function`, the `id` cannot be `null`.
+A function declaration. Note that unlike in the parent interface `Function`, the `id` cannot be `null`, except when this is the child of an `ExportDefaultDeclaration`.
 
 ## VariableDeclaration
 
@@ -1166,9 +1166,17 @@ An exported variable binding, e.g., `{foo}` in `export {foo}` or `{bar as foo}`
 ### ExportDefaultDeclaration
 
 ```js
+interface OptFunctionDeclaration <: FunctionDeclaration {
+  id: Identifier | null;
+}
+
+interface OptClasDeclaration <: ClassDeclaration {
+  id: Identifier | null;
+}
+
 interface ExportDefaultDeclaration <: ModuleDeclaration {
   type: "ExportDefaultDeclaration";
-  declaration: Declaration | Expression;
+  declaration: OptFunctionDeclaration | OptClassDeclaration | Expression;
 }
 ```
 
diff --git a/src/types.js b/src/types.js
index b42f72a154..e76d738994 100644
--- a/src/types.js
+++ b/src/types.js
@@ -266,11 +266,14 @@ export type ForOfStatement = ForInOfBase & {
 
 // Declarations
 
-export type FunctionDeclaration = FunctionBase & DeclarationBase & HasDecorators & {
+export type OptFunctionDeclaration = FunctionBase & DeclarationBase & HasDecorators & {
   type: "FunctionDeclaration";
-  id: Identifier;
 };
 
+export type FunctionDeclaration = OptFunctionDeclaration & {
+  id: Identifier;
+}
+
 export type VariableDeclaration = DeclarationBase & HasDecorators & {
   type: "VariableDeclaration";
   declarations: $ReadOnlyArray<VariableDeclarator>;
@@ -581,13 +584,16 @@ export type ClassProperty = ClassMemberBase & {
   readonly?: true;
 };
 
-export type ClassDeclaration = ClassBase & DeclarationBase & HasDecorators & {
+export type OptClassDeclaration = ClassBase & DeclarationBase & HasDecorators & {
   type: "ClassDeclaration";
-  id: Identifier;
   // TypeScript only
   abstract?: ?true;
 };
 
+export type ClassDeclaration = OptClassDeclaration & {
+  id: Identifier;
+};
+
 export type ClassExpression = ClassBase & { type: "ClassExpression" };
 
 export type MetaProperty = NodeBase & {
@@ -653,7 +659,7 @@ export type ExportSpecifier = NodeBase & {
 
 export type ExportDefaultDeclaration = NodeBase & {
   type: "ExportDefaultDeclaration";
-  declaration: Declaration | Expression;
+  declaration: OptFunctionDeclaration | OptClassDeclaration | Expression;
 };
 
 export type ExportAllDeclaration = NodeBase & {