diff --git a/packages/babel-parser/src/plugins/typescript/index.js b/packages/babel-parser/src/plugins/typescript/index.js
index 1b9b7f1f3e83..79fa83a35446 100644
--- a/packages/babel-parser/src/plugins/typescript/index.js
+++ b/packages/babel-parser/src/plugins/typescript/index.js
@@ -1039,7 +1039,7 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         const t: N.TsTypeAnnotation = this.startNode();
         this.expect(returnToken);
 
-        const asserts = this.tsTryParse(
+        const asserts = !!this.tsTryParse(
           this.tsParseTypePredicateAsserts.bind(this),
         );
 
diff --git a/packages/babel-parser/test/fixtures/typescript/arrow-function/predicate-types/output.json b/packages/babel-parser/test/fixtures/typescript/arrow-function/predicate-types/output.json
index 4cc69d94f780..69135a95cab8 100644
--- a/packages/babel-parser/test/fixtures/typescript/arrow-function/predicate-types/output.json
+++ b/packages/babel-parser/test/fixtures/typescript/arrow-function/predicate-types/output.json
@@ -31,7 +31,8 @@
                   "type": "TSStringKeyword",
                   "start":15,"end":21,"loc":{"start":{"line":1,"column":15},"end":{"line":1,"column":21}}
                 }
-              }
+              },
+              "asserts": false
             }
           },
           "id": null,
diff --git a/packages/babel-parser/test/fixtures/typescript/function/predicate-types/output.json b/packages/babel-parser/test/fixtures/typescript/function/predicate-types/output.json
index b834fb54ebb7..593fba67d38d 100644
--- a/packages/babel-parser/test/fixtures/typescript/function/predicate-types/output.json
+++ b/packages/babel-parser/test/fixtures/typescript/function/predicate-types/output.json
@@ -50,7 +50,8 @@
                 "type": "TSBooleanKeyword",
                 "start":25,"end":32,"loc":{"start":{"line":1,"column":25},"end":{"line":1,"column":32}}
               }
-            }
+            },
+            "asserts": false
           }
         },
         "body": {
@@ -66,6 +67,10 @@
         "expression": {
           "type": "FunctionExpression",
           "start":37,"end":70,"loc":{"start":{"line":2,"column":1},"end":{"line":2,"column":34}},
+          "extra": {
+            "parenthesized": true,
+            "parenStart": 36
+          },
           "id": null,
           "generator": false,
           "async": false,
@@ -102,7 +107,8 @@
                   "type": "TSBooleanKeyword",
                   "start":60,"end":67,"loc":{"start":{"line":2,"column":24},"end":{"line":2,"column":31}}
                 }
-              }
+              },
+              "asserts": false
             }
           },
           "body": {
@@ -110,10 +116,6 @@
             "start":68,"end":70,"loc":{"start":{"line":2,"column":32},"end":{"line":2,"column":34}},
             "body": [],
             "directives": []
-          },
-          "extra": {
-            "parenthesized": true,
-            "parenStart": 36
           }
         }
       }