--- a/m4/st_mtim.m4
+++ b/m4/st_mtim.m4
@@ -1,29 +1,30 @@
-#serial 2
+#serial 3
 
 dnl From Paul Eggert.
 
-# Define HAVE_ST_MTIM if struct stat has an st_mtim member.
-
-AC_DEFUN(AC_STRUCT_ST_MTIM,
- [AC_CACHE_CHECK([for st_mtim in struct stat], ac_cv_struct_st_mtim,
-   [AC_TRY_COMPILE([#include <sys/types.h>
-#include <sys/stat.h>], [struct stat s; s.st_mtim;],
-     ac_cv_struct_st_mtim=yes,
-     ac_cv_struct_st_mtim=no)])
+# Define ST_MTIM_NSEC to be the nanoseconds member of struct stat's st_mtim,
+# if it exists.
 
-  if test $ac_cv_struct_st_mtim = yes; then
-    if test x = y; then
-      # This code is deliberately never run via ./configure.
-      # FIXME: this is a hack to make autoheader put the corresponding
-      # HAVE_* undef for this symbol in config.h.in.  This saves me the
-      # trouble of having to add the #undef in acconfig.h manually.
-      AC_CHECK_FUNCS(ST_MTIM)
-    fi
-    # Defining it this way (rather than via AC_DEFINE) short-circuits the
-    # autoheader check -- autoheader doesn't know it's already been taken
-    # care of by the hack above.
-    ac_kludge=HAVE_ST_MTIM
-    AC_DEFINE_UNQUOTED($ac_kludge)
+AC_DEFUN(AC_STRUCT_ST_MTIM_NSEC,
+ [AC_CACHE_CHECK([for nanoseconds member of struct stat.st_mtim],
+   ac_cv_struct_st_mtim_nsec,
+   [ac_save_CPPFLAGS="$CPPFLAGS"
+    ac_cv_struct_st_mtim_nsec=no
+    # tv_nsec -- the usual case
+    # _tv_nsec -- Solaris 2.6, if
+    #	(defined _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED == 1
+    #	 && !defined __EXTENSIONS__)
+    # st__tim.tv_nsec -- UnixWare 2.1.2
+    for ac_val in tv_nsec _tv_nsec st__tim.tv_nsec; do
+      CPPFLAGS="$ac_save_CPPFLAGS -DST_MTIM_NSEC=$ac_val"
+      AC_TRY_COMPILE([#include <sys/types.h>
+#include <sys/stat.h>], [struct stat s; s.st_mtim.ST_MTIM_NSEC;],
+        [ac_cv_struct_st_mtim_nsec=$ac_val; break])
+    done
+    CPPFLAGS="$ac_save_CPPFLAGS"])
+
+  if test $ac_cv_struct_st_mtim_nsec != no; then
+    AC_DEFINE_UNQUOTED(ST_MTIM_NSEC, $ac_cv_struct_st_mtim_nsec)
   fi
  ]
 )