diff --git a/gtk/src/gtk_display_driver_opengl.cpp b/gtk/src/gtk_display_driver_opengl.cpp
index 698357a1..ccacf21e 100644
--- a/gtk/src/gtk_display_driver_opengl.cpp
+++ b/gtk/src/gtk_display_driver_opengl.cpp
@@ -170,7 +170,7 @@ S9xOpenGLDisplayDriver::update (int width, int height)
     w = allocation.width; h = allocation.height;
     S9xApplyAspect (x, y, w, h);
 
-    glViewport (x, allocation.height-y-h, w, h);
+    glViewport (x, allocation.height - y - h, w, h);
     window->set_mouseable_area (x, y, w, h);
 
     update_texture_size (width, height);