diff --git a/packages/babel-generator/test/index.js b/packages/babel-generator/test/index.js
index 99b5955222..ffb8811358 100644
--- a/packages/babel-generator/test/index.js
+++ b/packages/babel-generator/test/index.js
@@ -328,6 +328,23 @@ describe("programmatic generation", function() {
     );
   });
 
+  it("flow object exact", function() {
+    const objectStatement = t.objectTypeAnnotation(
+      [t.objectTypeProperty(t.identifier("bar"), t.stringTypeAnnotation())],
+      null,
+      null,
+      true,
+    );
+
+    const output = generate(objectStatement).code;
+    assert.equal(
+      output,
+      `{|
+  bar: string
+|}`,
+    );
+  });
+
   it("flow object indentation with empty leading ObjectTypeProperty", function() {
     const objectStatement = t.objectTypeAnnotation(
       [],
diff --git a/packages/babel-types/README.md b/packages/babel-types/README.md
index 2f2868c500..a48301c15c 100644
--- a/packages/babel-types/README.md
+++ b/packages/babel-types/README.md
@@ -1499,7 +1499,7 @@ Aliases: `UserWhitespacable`, `Property`, `ObjectMember`
 
 ### objectTypeAnnotation
 ```javascript
-t.objectTypeAnnotation(properties, indexers, callProperties)
+t.objectTypeAnnotation(properties, indexers, callProperties, exact)
 ```
 
 See also `t.isObjectTypeAnnotation(node, opts)` and `t.assertObjectTypeAnnotation(node, opts)`.
@@ -1509,7 +1509,7 @@ Aliases: `Flow`, `FlowType`
  - `properties`: `Array<ObjectTypeProperty | ObjectTypeSpreadProperty>` (required)
  - `indexers`: `Array<ObjectTypeIndexer>` (default: `null`)
  - `callProperties`: `Array<ObjectTypeCallProperty>` (default: `null`)
- - `exact`: `boolean` (default: `null`)
+ - `exact`: `boolean` (default: `false`)
 
 ---
 
diff --git a/packages/babel-types/src/definitions/flow.js b/packages/babel-types/src/definitions/flow.js
index 709d179db7..cbd75c7775 100644
--- a/packages/babel-types/src/definitions/flow.js
+++ b/packages/babel-types/src/definitions/flow.js
@@ -252,13 +252,17 @@ defineType("NumberTypeAnnotation", {
 defineType("ObjectTypeAnnotation", {
   visitor: ["properties", "indexers", "callProperties"],
   aliases: ["Flow", "FlowType"],
+  builder: ["properties", "indexers", "callProperties", "exact"],
   fields: {
     properties: validate(
       arrayOfType(["ObjectTypeProperty", "ObjectTypeSpreadProperty"]),
     ),
     indexers: validateOptional(arrayOfType("ObjectTypeIndexer")),
     callProperties: validateOptional(arrayOfType("ObjectTypeCallProperty")),
-    exact: validate(assertValueType("boolean")),
+    exact: {
+      validate: assertValueType("boolean"),
+      default: false,
+    },
   },
 });