diff --git a/configure.ac b/configure.ac
index 6fea3afcc8..41e24a3928 100644
--- a/configure.ac
+++ b/configure.ac
@@ -987,11 +987,13 @@ if test "x$enable_x11_backend" = xyes; then
 
   AC_MSG_CHECKING([if <X11/extensions/XIproto.h> is needed for xReply])
   AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <X11/Xlibint.h>]],
-                                     [[xReply *rep;]])],
+                                     [[xReply *rep = NULL;
+                                       rep = rep;]])],
                     [AC_MSG_RESULT([no])],
                     [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <X11/extensions/XIproto.h>
                                                           #include <X11/Xlibint.h>]],
-                                                        [[xReply *rep;]])],
+                                                        [[xReply *rep = NULL;
+                                                          rep = rep;]])],
                                        [AC_MSG_RESULT([yes])
                                         AC_DEFINE([NEED_XIPROTO_H_FOR_XREPLY], [1],
                                                   [Define if <X11/extensions/XIproto.h> needed for xReply])],