diff --git a/src/field.js b/src/field.js
index 05d89cae8..e0feb8b43 100644
--- a/src/field.js
+++ b/src/field.js
@@ -270,6 +270,9 @@ Field.prototype.resolve = function resolve() {
             this.typeDefault = null;
         else // instanceof Enum
             this.typeDefault = this.resolvedType.values[Object.keys(this.resolvedType.values)[0]]; // first defined
+    } else if (this.options && this.options.proto3_optional) {
+        // proto3 scalar value marked optional; should default to null
+        this.typeDefault = null;
     }
 
     // use explicitly set default value if present
diff --git a/tests/comp_optional.js b/tests/comp_optional.js
index fd12fa9a5..f0a5e50f6 100644
--- a/tests/comp_optional.js
+++ b/tests/comp_optional.js
@@ -22,5 +22,9 @@ tape.test("proto3 optional", function(test) {
     test.equal(Message.oneofs._optionalInt32.name, '_optionalInt32');
     test.deepEqual(Message.oneofs._optionalInt32.oneof, ['optionalInt32']);
 
+    var m = Message.create({});
+    test.strictEqual(m.regularInt32, 0);
+    test.strictEqual(m.optionalInt32, null);
+
     test.end();
 });