--- Makefile.in.old
+++ Makefile.in
@@ -743,7 +743,6 @@
 
 ACLOCAL_AMFLAGS = -I m4
 MOSTLYCLEANFILES = $(DX_CLEANFILES)
-POSIX_C_SOURCE = 200809L
 EXTRA_DIST = \
 	bootstrap \
 	ChangeLog \
@@ -762,7 +761,6 @@
 
 AM_CPPFLAGS = \
 	-D_ISOC99_SOURCE \
-	-D_POSIX_C_SOURCE=$(POSIX_C_SOURCE) \
 	-D_REENTRANT \
 	\
 	-I$(top_srcdir)/src \