configure.in: s/AC_AIX/AC_USE_SYSTEM_EXTENSIONS/
diff --git a/configure.in b/configure.in
index 855fa3b..12cb213 100644
--- a/configure.in
+++ b/configure.in
@@ -500,7 +500,7 @@
 
 
 # checks for UNIX variants that set C preprocessor variables
-AC_AIX
+AC_USE_SYSTEM_EXTENSIONS
 
 # Check for unsupported systems
 case $ac_sys_system/$ac_sys_release in