diff --git a/packages/babel-parser/src/types.js b/packages/babel-parser/src/types.js
index 8392a58db0f2..82815b1443d6 100644
--- a/packages/babel-parser/src/types.js
+++ b/packages/babel-parser/src/types.js
@@ -1227,6 +1227,7 @@ export type TsTypePredicate = TsTypeBase & {
   type: "TSTypePredicate",
   parameterName: Identifier | TsThisType,
   typeAnnotation: TsTypeAnnotation,
+  asserts?: boolean,
 };
 
 // `typeof` operator
diff --git a/packages/babel-types/src/definitions/typescript.js b/packages/babel-types/src/definitions/typescript.js
index bba8a5b73c8e..608ea8ab2207 100644
--- a/packages/babel-types/src/definitions/typescript.js
+++ b/packages/babel-types/src/definitions/typescript.js
@@ -175,11 +175,12 @@ defineType("TSTypeReference", {
 
 defineType("TSTypePredicate", {
   aliases: ["TSType"],
-  visitor: ["parameterName", "typeAnnotation", "asserts"],
+  visitor: ["parameterName", "typeAnnotation"],
+  builder: ["parameterName", "typeAnnotation", "asserts"],
   fields: {
     parameterName: validateType(["Identifier", "TSThisType"]),
     typeAnnotation: validateOptionalType("TSTypeAnnotation"),
-    asserts: validate(bool),
+    asserts: validateOptional(bool),
   },
 });