diff --git a/m4/gnulib-cache.m4 b/m4/gnulib-cache.m4
index f8f0304..b48f8de 100644
--- a/m4/gnulib-cache.m4
+++ b/m4/gnulib-cache.m4
@@ -41,6 +41,7 @@
 #  btowc \
 #  config-h \
 #  crc \
+#  extensions \
 #  getopt-gnu \
 #  gettext-h \
 #  gettimeofday \
@@ -69,6 +70,7 @@ gl_MODULES([
   btowc
   config-h
   crc
+  extensions
   getopt-gnu
   gettext-h
   gettimeofday
diff --git a/src/system.h b/src/system.h
index e3b59cd..8915b6d 100644
--- a/src/system.h
+++ b/src/system.h
@@ -47,14 +47,11 @@
 #  undef _XOPEN_SOURCE
 #  if defined(__sun) && defined(__SVR4)
 #    define _XOPEN_SOURCE	600	// Use SUSv3 on SunOS 5.x
-#    define __EXTENSIONS__	1	// ... with Solaris extensions
 #  else
 #    define _XOPEN_SOURCE	700	// Use SUSv4 everywhere else
 #  endif
 #endif
 
-#define _GNU_SOURCE		1	// Use GNU extensions as well
-
 
 // Headers defined by ISO/IEC 9899:1999 (C99)