diff --git a/src/Widget.cc b/src/Widget.cc
index 8674d1f..af24301 100644
--- a/src/Widget.cc
+++ b/src/Widget.cc
@@ -11,7 +11,7 @@ static VALUE Widget_render_begin(VALUE self)
     int width = FIX2INT(rb_iv_get(self, "@width"));
     int height = FIX2INT(rb_iv_get(self, "@height"));
 
-    glViewport(x, y, width, height);
+    glScissor(x, y, width, height);
 
     return Qnil;
 }
diff --git a/src/Window.cc b/src/Window.cc
index 18e4b7c..7002ccc 100644
--- a/src/Window.cc
+++ b/src/Window.cc
@@ -85,6 +85,8 @@ static void Init_OpenGL()
         rb_raise(rb_eRuntimeError, "OpenGL 3.0 is not supported");
     }
 
+    glEnable(GL_SCISSOR_TEST);
+
     initialized = true;
 }