diff --git a/src/cairo-directfb.h b/src/cairo-directfb.h
index 845f3de68..795a0dc16 100644
--- a/src/cairo-directfb.h
+++ b/src/cairo-directfb.h
@@ -48,5 +48,8 @@ cairo_directfb_surface_create (IDirectFB *dfb,IDirectFBSurface *surface);
 
 CAIRO_END_DECLS
 
+#else  /*CAIRO_HAS_DIRECTFB_SURFACE*/
+# error Cairo was not compiled with support for the directfb backend
 #endif /*CAIRO_HAS_DIRECTFB_SURFACE*/
+
 #endif /*CAIRO_DIRECTFB_H*/
diff --git a/src/cairo-os2.h b/src/cairo-os2.h
index 3e1b4aad4..6a6c04d5b 100644
--- a/src/cairo-os2.h
+++ b/src/cairo-os2.h
@@ -194,6 +194,8 @@ cairo_os2_surface_set_manual_window_refresh (cairo_surface_t *surface,
 cairo_public cairo_bool_t
 cairo_os2_surface_get_manual_window_refresh (cairo_surface_t *surface);
 
+#else  /* CAIRO_HAS_OS2_SURFACE */
+# error Cairo was not compiled with support for the OS/2 backend
 #endif /* CAIRO_HAS_OS2_SURFACE */
 
 CAIRO_END_DECLS