diff --git a/freeglut/freeglut/ChangeLog b/freeglut/freeglut/ChangeLog
index a4a103a..e28f1e6 100644
--- a/freeglut/freeglut/ChangeLog
+++ b/freeglut/freeglut/ChangeLog
@@ -1123,3 +1123,6 @@ extensions.
 for some bit-fiddling, anyway.
 
 (292) Avoid gcc warnings for some joystick code (e.g. on Solaris).
+
+(293) Improve autoconf magic: To detect headers like GL/gl.h, it might be
+necessary to temporarily use the X11 flags found by AC_PATH_XTRA.
diff --git a/freeglut/freeglut/configure.ac b/freeglut/freeglut/configure.ac
index 440c2db..5daea87 100644
--- a/freeglut/freeglut/configure.ac
+++ b/freeglut/freeglut/configure.ac
@@ -40,13 +40,12 @@ AC_SUBST([EXPORT_FLAGS])
 
 # Checks for header files.
 AC_HEADER_STDC
+save_CPPFLAGS="$CPPFLAGS"
+CPPFLAGS="$CPPFLAGS $X_CFLAGS"
 AC_CHECK_HEADERS([GL/gl.h GL/glu.h GL/glx.h fcntl.h limits.h sys/ioctl.h sys/param.h sys/time.h])
 AC_HEADER_TIME
-
-save_CFLAGS="$CFLAGS"
-CFLAGS="$CFLAGS $X_CFLAGS"
 AC_CHECK_HEADERS([X11/extensions/xf86vmode.h], [], [], [#include <X11/Xlib.h>])
-CFLAGS="$save_CFLAGS"
+CPPFLAGS="$save_CPPFLAGS"
 
 # Checks for library functions.
 AC_PROG_GCC_TRADITIONAL