diff --git a/compiler/prelude/jsmapping.go b/compiler/prelude/jsmapping.go
index 24cdf8ed3..ce0691b5a 100644
--- a/compiler/prelude/jsmapping.go
+++ b/compiler/prelude/jsmapping.go
@@ -181,6 +181,13 @@ var $internalize = function(v, t, recv) {
   if (t === $jsObjectPtr.elem) {
     $panic(new $String("cannot internalize js.Object, use *js.Object instead"));
   }
+  var timePkg = $packages["time"];
+  if (timePkg !== undefined && t === timePkg.Time) {
+    if (!(v !== null && v !== undefined && v.constructor === Date)) {
+      $panic(new $String("cannot internalize time.Time from " + typeof v + ", must be Date"));
+    }
+    return timePkg.Unix(new $Int64(0, 0), new $Int64(0, v.getTime() * 1000000));
+  }
   switch (t.kind) {
   case $kindBool:
     return !!v;
@@ -270,12 +277,11 @@ var $internalize = function(v, t, recv) {
     case Boolean:
       return new $Bool(!!v);
     case Date:
-      var timePkg = $packages["time"];
       if (timePkg === undefined) {
         /* time package is not present, internalize as &js.Object{Date} so it can be externalized into original Date. */
         return new $jsObjectPtr(v);
       }
-      return new timePkg.Time(timePkg.Unix(new $Int64(0, 0), new $Int64(0, v.getTime() * 1000000)));
+      return new timePkg.Time($internalize(v, timePkg.Time));
     case Function:
       var funcType = $funcType([$sliceType($emptyInterface)], [$jsObjectPtr], true);
       return new funcType($internalize(v, funcType));
diff --git a/js/js_test.go b/js/js_test.go
index 754fb1a1b..189776525 100644
--- a/js/js_test.go
+++ b/js/js_test.go
@@ -287,6 +287,17 @@ func TestDate(t *testing.T) {
 	}
 }
 
+// https://github.com/gopherjs/gopherjs/issues/287
+func TestInternalizeDate(t *testing.T) {
+	var a = time.Unix(0, (123 * time.Millisecond).Nanoseconds())
+	var b time.Time
+	js.Global.Set("internalizeDate", func(t time.Time) { b = t })
+	js.Global.Call("eval", "(internalizeDate(new Date(123)))")
+	if a != b {
+		t.Fail()
+	}
+}
+
 func TestEquality(t *testing.T) {
 	if js.Global.Get("Array") != js.Global.Get("Array") || js.Global.Get("Array") == js.Global.Get("String") {
 		t.Fail()
@@ -480,6 +491,21 @@ func TestNewArrayBuffer(t *testing.T) {
 	}
 }
 
+func TestInternalizeExternalizeNull(t *testing.T) {
+	type S struct {
+		*js.Object
+	}
+	r := js.Global.Call("eval", "(function(f) { return f(null); })").Invoke(func(s S) S {
+		if s.Object != nil {
+			t.Fail()
+		}
+		return s
+	})
+	if r != nil {
+		t.Fail()
+	}
+}
+
 func TestInternalizeExternalizeUndefined(t *testing.T) {
 	type S struct {
 		*js.Object