diff --git a/gdk/gdkwindow.c b/gdk/gdkwindow.c
index 8191e0c14e..6d48080294 100644
--- a/gdk/gdkwindow.c
+++ b/gdk/gdkwindow.c
@@ -42,6 +42,9 @@
 
 #include <math.h>
 
+/* for the use of round() */
+#include "fallback-c89.c"
+
 #undef DEBUG_WINDOW_PRINTING
 
 
diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index 37460e3419..5716a04ae0 100644
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -66,6 +66,9 @@
 #include "gtktypebuiltins.h"
 #include "a11y/gtkwidgetaccessible.h"
 
+/* for the use of round() */
+#include "fallback-c89.c"
+
 /**
  * SECTION:gtkwidget
  * @Short_description: Base class for all widgets