--- a/configure.ac
+++ b/configure.ac
@@ -6,6 +6,8 @@
 
 AC_PREREQ(2.50)
 
+AC_USE_SYSTEM_EXTENSIONS
+
 AM_PROG_CC_C_O
 AC_PROG_CPP
 AC_PROG_LIBTOOL
@@ -172,6 +174,12 @@
 AC_TRY_COMPILE(
  [#define _LARGEFILE64_SOURCE
   #define _LARGEFILE_SOURCE
+  #include <stdio.h>],
+ [fpos64_t x; long long int y = x.__lldata;],
+ [ac_v_fpos64_t="(x).__lldata"])
+AC_TRY_COMPILE(
+ [#define _LARGEFILE64_SOURCE
+  #define _LARGEFILE_SOURCE
   #include <stdio.h>],
  [fpos64_t x; long long int y = (long long int)x;],
  [ac_v_fpos64_t="(x)"])