diff --git a/cli/pbjs.js b/cli/pbjs.js
index 6b69397f3..801f40144 100644
--- a/cli/pbjs.js
+++ b/cli/pbjs.js
@@ -41,7 +41,7 @@ exports.main = function main(args, callback) {
             "force-message": "strict-message"
         },
         string: [ "target", "out", "path", "wrap", "dependency", "root", "lint" ],
-        boolean: [ "create", "encode", "decode", "verify", "convert", "delimited", "beautify", "comments", "service", "es6", "sparse", "keep-case", "force-long", "force-number", "force-enum-string", "force-message" ],
+        boolean: [ "create", "encode", "decode", "verify", "convert", "delimited", "beautify", "comments", "service", "es6", "sparse", "keep-case", "force-long", "force-number", "force-enum-string", "force-message", "null-defaults" ],
         default: {
             target: "json",
             create: true,
@@ -59,7 +59,8 @@ exports.main = function main(args, callback) {
             "force-long": false,
             "force-number": false,
             "force-enum-string": false,
-            "force-message": false
+            "force-message": false,
+            "null-defaults": false,
         }
     });
 
@@ -139,6 +140,8 @@ exports.main = function main(args, callback) {
                 "  --force-number   Enforces the use of 'number' for s-/u-/int64 and s-/fixed64 fields.",
                 "  --force-message  Enforces the use of message instances instead of plain objects.",
                 "",
+                "  --null-defaults  Default value for optional fields is null instead of zero value.",
+                "",
                 "usage: " + chalk.bold.green("pbjs") + " [options] file1.proto file2.json ..." + chalk.gray("  (or pipe)  ") + "other | " + chalk.bold.green("pbjs") + " [options] -",
                 ""
             ].join("\n"));
diff --git a/cli/targets/static.js b/cli/targets/static.js
index a738f3585..4d6e6a102 100644
--- a/cli/targets/static.js
+++ b/cli/targets/static.js
@@ -394,7 +394,7 @@ function buildType(ref, type) {
         if (config.comments) {
             push("");
             var jsType = toJsType(field);
-            if (field.optional && !field.map && !field.repeated && field.resolvedType instanceof Type || field.partOf)
+            if (field.optional && !field.map && !field.repeated && (field.resolvedType instanceof Type || config["null-defaults"]) || field.partOf)
                 jsType = jsType + "|null|undefined";
             pushComment([
                 field.comment || type.name + " " + field.name + ".",
@@ -410,7 +410,7 @@ function buildType(ref, type) {
             push(escapeName(type.name) + ".prototype" + prop + " = $util.emptyArray;"); // overwritten in constructor
         else if (field.map)
             push(escapeName(type.name) + ".prototype" + prop + " = $util.emptyObject;"); // overwritten in constructor
-        else if (field.partOf)
+        else if (field.partOf || (field.optional && config["null-defaults"]))
             push(escapeName(type.name) + ".prototype" + prop + " = null;"); // do not set default value for oneof members
         else if (field.long)
             push(escapeName(type.name) + ".prototype" + prop + " = $util.Long ? $util.Long.fromBits("
diff --git a/tests/cli.js b/tests/cli.js
index a73ac0181..177d721ae 100644
--- a/tests/cli.js
+++ b/tests/cli.js
@@ -5,7 +5,7 @@ var path = require("path");
 var Module = require("module");
 var protobuf = require("..");
 
-tape.test("pbjs generates static code", function(test) {
+function cliTest(test, testFunc) {
     // pbjs does not seem to work with Node v4, so skip this test if we're running on it
     if (process.versions.node.match(/^4\./)) {
         test.end();
@@ -23,54 +23,133 @@ tape.test("pbjs generates static code", function(test) {
     };
     require.cache.protobufjs = require.cache[path.resolve("index.js")];
 
-    var staticTarget = require("../cli/targets/static");
-
-    var root = protobuf.loadSync("tests/data/cli/test.proto");
-    root.resolveAll();
-
-    staticTarget(root, {
-        create: true,
-        decode: true,
-        encode: true,
-        convert: true,
-    }, function(err, jsCode) {
-        test.error(err, 'static code generation worked');
-
-        // jsCode is the generated code; we'll eval it
-        // (since this is what we normally does with the code, right?)
-        // This is a test code. Do not use this in production.
-        var $protobuf = protobuf;
-        eval(jsCode);
-
-        var OneofContainer = protobuf.roots.default.OneofContainer;
-        var Message = protobuf.roots.default.Message;
-        test.ok(OneofContainer, "type is loaded");
-        test.ok(Message, "type is loaded");
-
-        // Check that fromObject and toObject work for plain object
-        var obj = {
-            messageInOneof: {
-                value: 42,
-            },
-            regularField: "abc",
-        };
-        var obj1 = OneofContainer.toObject(OneofContainer.fromObject(obj));
-        test.deepEqual(obj, obj1, "fromObject and toObject work for plain object");
-
-        // Check that dynamic fromObject and toObject work for static instance
+    try {
+        testFunc();
+    } finally {
+        // Rollback all the require() related mess we made
+        delete require.cache.protobufjs;
+        Module._resolveFilename = savedResolveFilename;
+    }
+}
+
+tape.test("pbjs generates static code", function(test) {
+    cliTest(test, function() {
         var root = protobuf.loadSync("tests/data/cli/test.proto");
-        var OneofContainerDynamic = root.lookup("OneofContainer");
-        var instance = new OneofContainer();
-        instance.messageInOneof = new Message();
-        instance.messageInOneof.value = 42;
-        instance.regularField = "abc";
-        var instance1 = OneofContainerDynamic.toObject(OneofContainerDynamic.fromObject(instance));
-        test.deepEqual(instance, instance1, "fromObject and toObject work for instance of the static type");
-        
-        test.end();
+        root.resolveAll();
+
+        var staticTarget = require("../cli/targets/static");
+
+        staticTarget(root, {
+            create: true,
+            decode: true,
+            encode: true,
+            convert: true,
+        }, function(err, jsCode) {
+            test.error(err, 'static code generation worked');
+
+            // jsCode is the generated code; we'll eval it
+            // (since this is what we normally does with the code, right?)
+            // This is a test code. Do not use this in production.
+            var $protobuf = protobuf;
+            eval(jsCode);
+
+            var OneofContainer = protobuf.roots.default.OneofContainer;
+            var Message = protobuf.roots.default.Message;
+            test.ok(OneofContainer, "type is loaded");
+            test.ok(Message, "type is loaded");
+
+            // Check that fromObject and toObject work for plain object
+            var obj = {
+                messageInOneof: {
+                    value: 42,
+                },
+                regularField: "abc",
+            };
+            var obj1 = OneofContainer.toObject(OneofContainer.fromObject(obj));
+            test.deepEqual(obj, obj1, "fromObject and toObject work for plain object");
+
+            // Check that dynamic fromObject and toObject work for static instance
+            var root = protobuf.loadSync("tests/data/cli/test.proto");
+            var OneofContainerDynamic = root.lookup("OneofContainer");
+            var instance = new OneofContainer();
+            instance.messageInOneof = new Message();
+            instance.messageInOneof.value = 42;
+            instance.regularField = "abc";
+            var instance1 = OneofContainerDynamic.toObject(OneofContainerDynamic.fromObject(instance));
+            test.deepEqual(instance, instance1, "fromObject and toObject work for instance of the static type");
+
+            test.end();
+        });
     });
+});
+
+tape.test("without null-defaults, absent optional fields have zero values", function(test) {
+    cliTest(test, function() {
+        var root = protobuf.loadSync("tests/data/cli/null-defaults.proto");
+        root.resolveAll();
+
+        var staticTarget = require("../cli/targets/static");
 
-    // Rollback all the require() related mess we made
-    delete require.cache.protobufjs;
-    Module._resolveFilename = savedResolveFilename;
+        staticTarget(root, {
+            create: true,
+            decode: true,
+            encode: true,
+            convert: true,
+        }, function(err, jsCode) {
+            test.error(err, 'static code generation worked');
+
+            // jsCode is the generated code; we'll eval it
+            // (since this is what we normally does with the code, right?)
+            // This is a test code. Do not use this in production.
+            var $protobuf = protobuf;
+            eval(jsCode);
+
+            var OptionalFields = protobuf.roots.default.OptionalFields;
+            test.ok(OptionalFields, "type is loaded");
+
+            // Check default values
+            var msg = OptionalFields.fromObject({});
+            test.equal(msg.a, null, "default submessage is null");
+            test.equal(msg.b, "", "default string is empty");
+            test.equal(msg.c, 0, "default integer is 0");
+
+            test.end();
+        });
+    });
+});
+
+tape.test("with null-defaults, absent optional fields have null values", function(test) {
+    cliTest(test, function() {
+        var root = protobuf.loadSync("tests/data/cli/null-defaults.proto");
+        root.resolveAll();
+
+        var staticTarget = require("../cli/targets/static");
+
+        staticTarget(root, {
+            create: true,
+            decode: true,
+            encode: true,
+            convert: true,
+            "null-defaults": true,
+        }, function(err, jsCode) {
+            test.error(err, 'static code generation worked');
+
+            // jsCode is the generated code; we'll eval it
+            // (since this is what we normally does with the code, right?)
+            // This is a test code. Do not use this in production.
+            var $protobuf = protobuf;
+            eval(jsCode);
+
+            var OptionalFields = protobuf.roots.default.OptionalFields;
+            test.ok(OptionalFields, "type is loaded");
+
+            // Check default values
+            var msg = OptionalFields.fromObject({});
+            test.equal(msg.a, null, "default submessage is null");
+            test.equal(msg.b, null, "default string is null");
+            test.equal(msg.c, null, "default integer is null");
+
+            test.end();
+        });
+    });
 });
diff --git a/tests/data/cli/null-defaults.proto b/tests/data/cli/null-defaults.proto
new file mode 100644
index 000000000..6a140b1e2
--- /dev/null
+++ b/tests/data/cli/null-defaults.proto
@@ -0,0 +1,11 @@
+syntax = "proto2";
+
+message OptionalFields {
+  message SubMessage {
+    required string a = 1;
+  }
+
+  optional SubMessage a = 1;
+  optional string b = 2;
+  optional uint32 c = 3;
+}