diff --git a/cogl/cogl/cogl-onscreen.c b/cogl/cogl/cogl-onscreen.c
index 214e0d9df..6aefd531c 100644
--- a/cogl/cogl/cogl-onscreen.c
+++ b/cogl/cogl/cogl-onscreen.c
@@ -414,16 +414,14 @@ int
 cogl_onscreen_get_buffer_age (CoglOnscreen *onscreen)
 {
   CoglFramebuffer *framebuffer = COGL_FRAMEBUFFER (onscreen);
-  const CoglWinsysVtable *winsys;
+  CoglOnscreenClass *klass = COGL_ONSCREEN_GET_CLASS (onscreen);
 
   g_return_val_if_fail (COGL_IS_ONSCREEN (framebuffer), 0);
 
-  winsys = _cogl_framebuffer_get_winsys (framebuffer);
-
-  if (!winsys->onscreen_get_buffer_age)
+  if (!klass->get_buffer_age)
     return 0;
 
-  return winsys->onscreen_get_buffer_age (onscreen);
+  return klass->get_buffer_age (onscreen);
 }
 
 gboolean
diff --git a/cogl/cogl/cogl-onscreen.h b/cogl/cogl/cogl-onscreen.h
index 3b761cd3d..7284e04d5 100644
--- a/cogl/cogl/cogl-onscreen.h
+++ b/cogl/cogl/cogl-onscreen.h
@@ -79,6 +79,8 @@ struct _CoglOnscreenClass
                                CoglFrameInfo  *info,
                                gpointer        user_data,
                                GError        **error);
+
+  int (* get_buffer_age) (CoglOnscreen *onscreen);
 };
 
 #define COGL_SCANOUT_ERROR (cogl_scanout_error_quark ())
diff --git a/cogl/cogl/winsys/cogl-onscreen-egl.c b/cogl/cogl/winsys/cogl-onscreen-egl.c
index 3bfa4ba0e..7e170f35a 100644
--- a/cogl/cogl/winsys/cogl-onscreen-egl.c
+++ b/cogl/cogl/winsys/cogl-onscreen-egl.c
@@ -163,8 +163,8 @@ cogl_onscreen_egl_bind (CoglOnscreen *onscreen)
 #define EGL_BUFFER_AGE_EXT 0x313D
 #endif
 
-int
-_cogl_winsys_onscreen_egl_get_buffer_age (CoglOnscreen *onscreen)
+static int
+cogl_onscreen_egl_get_buffer_age (CoglOnscreen *onscreen)
 {
   CoglOnscreenEgl *onscreen_egl = COGL_ONSCREEN_EGL (onscreen);
   CoglOnscreenEglPrivate *priv =
@@ -354,4 +354,5 @@ cogl_onscreen_egl_class_init (CoglOnscreenEglClass *klass)
   onscreen_class->swap_buffers_with_damage =
     cogl_onscreen_egl_swap_buffers_with_damage;
   onscreen_class->swap_region = cogl_onscreen_egl_swap_region;
+  onscreen_class->get_buffer_age = cogl_onscreen_egl_get_buffer_age;
 }
diff --git a/cogl/cogl/winsys/cogl-onscreen-egl.h b/cogl/cogl/winsys/cogl-onscreen-egl.h
index 6843439f2..e152e1d6a 100644
--- a/cogl/cogl/winsys/cogl-onscreen-egl.h
+++ b/cogl/cogl/winsys/cogl-onscreen-egl.h
@@ -41,9 +41,6 @@ struct _CoglOnscreenEglClass
   CoglOnscreenClass parent_class;
 };
 
-int
-_cogl_winsys_onscreen_egl_get_buffer_age (CoglOnscreen *onscreen);
-
 COGL_EXPORT void
 cogl_onscreen_egl_set_platform (CoglOnscreenEgl *onscreen_egl,
                                 gpointer         platform);
diff --git a/cogl/cogl/winsys/cogl-onscreen-glx.c b/cogl/cogl/winsys/cogl-onscreen-glx.c
index 54e9146f1..dd33f622c 100644
--- a/cogl/cogl/winsys/cogl-onscreen-glx.c
+++ b/cogl/cogl/winsys/cogl-onscreen-glx.c
@@ -517,8 +517,8 @@ _cogl_winsys_get_vsync_counter (CoglContext *ctx)
 #define GLX_BACK_BUFFER_AGE_EXT 0x20F4
 #endif
 
-int
-_cogl_winsys_onscreen_glx_get_buffer_age (CoglOnscreen *onscreen)
+static int
+cogl_onscreen_glx_get_buffer_age (CoglOnscreen *onscreen)
 {
   CoglOnscreenGlx *onscreen_glx = COGL_ONSCREEN_GLX (onscreen);
   CoglFramebuffer *framebuffer = COGL_FRAMEBUFFER (onscreen);
@@ -1112,4 +1112,5 @@ cogl_onscreen_glx_class_init (CoglOnscreenGlxClass *klass)
   onscreen_class->swap_buffers_with_damage =
     cogl_onscreen_glx_swap_buffers_with_damage;
   onscreen_class->swap_region = cogl_onscreen_glx_swap_region;
+  onscreen_class->get_buffer_age = cogl_onscreen_glx_get_buffer_age;
 }
diff --git a/cogl/cogl/winsys/cogl-onscreen-glx.h b/cogl/cogl/winsys/cogl-onscreen-glx.h
index 81ac7be08..1051cb231 100644
--- a/cogl/cogl/winsys/cogl-onscreen-glx.h
+++ b/cogl/cogl/winsys/cogl-onscreen-glx.h
@@ -41,9 +41,6 @@ cogl_onscreen_glx_new (CoglContext *context,
                        int          width,
                        int          height);
 
-int
-_cogl_winsys_onscreen_glx_get_buffer_age (CoglOnscreen *onscreen);
-
 void
 cogl_onscreen_glx_resize (CoglOnscreen    *onscreen,
                           XConfigureEvent *configure_event);
diff --git a/cogl/cogl/winsys/cogl-winsys-egl.c b/cogl/cogl/winsys/cogl-winsys-egl.c
index fb2ab4be7..6e66041fa 100644
--- a/cogl/cogl/winsys/cogl-winsys-egl.c
+++ b/cogl/cogl/winsys/cogl-winsys-egl.c
@@ -636,7 +636,6 @@ static CoglWinsysVtable _cogl_winsys_vtable =
     .display_destroy = _cogl_winsys_display_destroy,
     .context_init = _cogl_winsys_context_init,
     .context_deinit = _cogl_winsys_context_deinit,
-    .onscreen_get_buffer_age = _cogl_winsys_onscreen_egl_get_buffer_age,
 
 #if defined(EGL_KHR_fence_sync) || defined(EGL_KHR_reusable_sync)
     .fence_add = _cogl_winsys_fence_add,
diff --git a/cogl/cogl/winsys/cogl-winsys-glx.c b/cogl/cogl/winsys/cogl-winsys-glx.c
index df60c1986..3e90b6ec6 100644
--- a/cogl/cogl/winsys/cogl-winsys-glx.c
+++ b/cogl/cogl/winsys/cogl-winsys-glx.c
@@ -1469,7 +1469,6 @@ static CoglWinsysVtable _cogl_winsys_vtable =
     .context_init = _cogl_winsys_context_init,
     .context_deinit = _cogl_winsys_context_deinit,
     .context_get_clock_time = _cogl_winsys_get_clock_time,
-    .onscreen_get_buffer_age = _cogl_winsys_onscreen_glx_get_buffer_age,
 
     /* X11 tfp support... */
     /* XXX: instead of having a rather monolithic winsys vtable we could
diff --git a/cogl/cogl/winsys/cogl-winsys-private.h b/cogl/cogl/winsys/cogl-winsys-private.h
index dc150752a..788573f94 100644
--- a/cogl/cogl/winsys/cogl-winsys-private.h
+++ b/cogl/cogl/winsys/cogl-winsys-private.h
@@ -32,7 +32,6 @@
 #define __COGL_WINSYS_PRIVATE_H
 
 #include "cogl-renderer.h"
-#include "cogl-onscreen.h"
 #include "cogl-scanout.h"
 
 #ifdef COGL_HAS_XLIB_SUPPORT
@@ -109,9 +108,6 @@ typedef struct _CoglWinsysVtable
   int64_t
   (*context_get_clock_time) (CoglContext *context);
 
-  int
-  (*onscreen_get_buffer_age) (CoglOnscreen *onscreen);
-
 #ifdef COGL_HAS_XLIB_SUPPORT
   gboolean
   (*texture_pixmap_x11_create) (CoglTexturePixmapX11 *tex_pixmap);