diff --git a/proto/x11proto/aclocal.m4 b/proto/x11proto/aclocal.m4
index 02b354806..08d7e4ac1 100644
--- a/proto/x11proto/aclocal.m4
+++ b/proto/x11proto/aclocal.m4
@@ -687,6 +687,41 @@ AC_DEFUN([_AM_IF_OPTION],
 # ---------------
 AC_DEFUN([AM_SANITY_CHECK],
 [AC_MSG_CHECKING([whether build environment is sane])
+# Just in case
+sleep 1
+echo timestamp > conftest.file
+# Do `set' in a subshell so we don't clobber the current shell's
+# arguments.  Must try -L first in case configure is actually a
+# symlink; some systems play weird games with the mod time of symlinks
+# (eg FreeBSD returns the mod time of the symlink's containing
+# directory).
+if (
+   set X `ls -Lt $srcdir/configure conftest.file 2> /dev/null`
+   if test "$[*]" = "X"; then
+      # -L didn't work.
+      set X `ls -t $srcdir/configure conftest.file`
+   fi
+   rm -f conftest.file
+   if test "$[*]" != "X $srcdir/configure conftest.file" \
+      && test "$[*]" != "X conftest.file $srcdir/configure"; then
+
+      # If neither matched, then we have a broken ls.  This can happen
+      # if, for instance, CONFIG_SHELL is bash and it inherits a
+      # broken ls alias from the environment.  This has actually
+      # happened.  Such a system could not be considered "sane".
+      AC_MSG_ERROR([ls -t appears to fail.  Make sure there is not a broken
+alias in your environment])
+   fi
+
+   test "$[2]" = conftest.file
+   )
+then
+   # Ok.
+   :
+else
+   AC_MSG_ERROR([newly created file is older than distributed files!
+Check your system clock])
+fi
 AC_MSG_RESULT(yes)])
 
 # Copyright (C) 2001, 2003, 2005  Free Software Foundation, Inc.
diff --git a/proto/x11proto/configure b/proto/x11proto/configure
index 07240c0d6..4c55d9b4f 100644
--- a/proto/x11proto/configure
+++ b/proto/x11proto/configure
@@ -1394,6 +1394,47 @@ test -z "$INSTALL_DATA" && INSTALL_DATA='${INSTALL} -m 644'
 
 echo "$as_me:$LINENO: checking whether build environment is sane" >&5
 echo $ECHO_N "checking whether build environment is sane... $ECHO_C" >&6
+# Just in case
+sleep 1
+echo timestamp > conftest.file
+# Do `set' in a subshell so we don't clobber the current shell's
+# arguments.  Must try -L first in case configure is actually a
+# symlink; some systems play weird games with the mod time of symlinks
+# (eg FreeBSD returns the mod time of the symlink's containing
+# directory).
+if (
+   set X `ls -Lt $srcdir/configure conftest.file 2> /dev/null`
+   if test "$*" = "X"; then
+      # -L didn't work.
+      set X `ls -t $srcdir/configure conftest.file`
+   fi
+   rm -f conftest.file
+   if test "$*" != "X $srcdir/configure conftest.file" \
+      && test "$*" != "X conftest.file $srcdir/configure"; then
+
+      # If neither matched, then we have a broken ls.  This can happen
+      # if, for instance, CONFIG_SHELL is bash and it inherits a
+      # broken ls alias from the environment.  This has actually
+      # happened.  Such a system could not be considered "sane".
+      { { echo "$as_me:$LINENO: error: ls -t appears to fail.  Make sure there is not a broken
+alias in your environment" >&5
+echo "$as_me: error: ls -t appears to fail.  Make sure there is not a broken
+alias in your environment" >&2;}
+   { (exit 1); exit 1; }; }
+   fi
+
+   test "$2" = conftest.file
+   )
+then
+   # Ok.
+   :
+else
+   { { echo "$as_me:$LINENO: error: newly created file is older than distributed files!
+Check your system clock" >&5
+echo "$as_me: error: newly created file is older than distributed files!
+Check your system clock" >&2;}
+   { (exit 1); exit 1; }; }
+fi
 echo "$as_me:$LINENO: result: yes" >&5
 echo "${ECHO_T}yes" >&6
 test "$program_prefix" != NONE &&