diff --git a/src/main/scala/ocelot/desktop/graphics/Viewport3D.scala b/src/main/scala/ocelot/desktop/graphics/Viewport3D.scala
index 482ea87..dc819a6 100644
--- a/src/main/scala/ocelot/desktop/graphics/Viewport3D.scala
+++ b/src/main/scala/ocelot/desktop/graphics/Viewport3D.scala
@@ -8,7 +8,7 @@ import org.lwjgl.opengl.{ARBFramebufferObject, GL11, GL21, GL30}
 
 import scala.collection.mutable
 
-class Viewport3D(val width: Int, var height: Int) extends Resource with Logging {
+class Viewport3D(width: Int, height: Int) extends Resource with Logging {
   private[graphics] val textureColor = new Texture(width, height, GL21.GL_SRGB8, GL11.GL_UNSIGNED_BYTE, GL11.GL_RGB)
   private val textureDepth = new Texture(width, height, GL11.GL_DEPTH_COMPONENT, GL11.GL_FLOAT)
 
diff --git a/src/main/scala/ocelot/desktop/ui/widget/Viewport3DWidget.scala b/src/main/scala/ocelot/desktop/ui/widget/Viewport3DWidget.scala
index 3d539bc..3d9f3c9 100644
--- a/src/main/scala/ocelot/desktop/ui/widget/Viewport3DWidget.scala
+++ b/src/main/scala/ocelot/desktop/ui/widget/Viewport3DWidget.scala
@@ -27,7 +27,11 @@ abstract class Viewport3DWidget extends Widget with DragHandler with HoverHandle
 
   protected def createScene(): Scene3D
 
-  private lazy val viewport = new Viewport3D(600, 400)
+  // XXX: the viewport's dimensions must be kept outside the viewport object itself: see #121
+  private val viewportWidth = 600
+  private val viewportHeight = 400
+
+  private lazy val viewport = new Viewport3D(viewportWidth, viewportHeight)
   private var viewportDisposed = false // extra safety
 
   protected val camera: Camera3D = new Camera3D()
@@ -55,14 +59,14 @@ abstract class Viewport3DWidget extends Widget with DragHandler with HoverHandle
 
   override protected val layout: Layout = new CopyLayout(this)
 
-  override def minimumSize: Size2D = Size2D(viewport.width + 4, viewport.height + 4)
+  override def minimumSize: Size2D = Size2D(viewportWidth + 4, viewportHeight + 4)
 
-  override def maximumSize: Size2D = Size2D(viewport.width + 4, viewport.height + 4)
+  override def maximumSize: Size2D = Size2D(viewportWidth + 4, viewportHeight + 4)
 
   children :+= new PaddingBox(new Widget {
-    override def minimumSize: Size2D = Size2D(viewport.width, viewport.height)
+    override def minimumSize: Size2D = Size2D(viewportWidth, viewportHeight)
 
-    override def maximumSize: Size2D = Size2D(viewport.width, viewport.height)
+    override def maximumSize: Size2D = Size2D(viewportWidth, viewportHeight)
 
     override def draw(g: Graphics): Unit = {
       DrawUtils.panel(g, bounds.x - 2, bounds.y - 2, bounds.w + 4, bounds.h + 4)