diff --git a/configure.in b/configure.in
index 5166ca4..faff15e 100644
--- a/configure.in
+++ b/configure.in
@@ -24,8 +24,7 @@ CFLAGS="$CFLAGS -D_XOPEN_SOURCE"
 CFLAGS="$CFLAGS -D__EXTENSIONS__"
 
 dnl Needed on some glibc systems
-CFLAGS="$CFLAGS -D_BSD_SOURCE"
-CFLAGS="$CFLAGS -D_ISO9X_SOURCE"
+CFLAGS="$CFLAGS -D_GNU_SOURCE"
 
 dnl Needed on Digital Unix
 CFLAGS="$CFLAGS -D_OSF_SOURCE"