diff --git a/src/dcfg.c b/src/dcfg.c
index 78bc0cd..a1ccec6 100644
--- a/src/dcfg.c
+++ b/src/dcfg.c
@@ -11,6 +11,9 @@
 #	endif
 #	define _XOPEN_SOURCE 200809L
 #else
+#	ifdef _POSIX_C_SOURCE
+#		undef _POSIX_C_SOURCE
+#	endif
 #	define _POSIX_C_SOURCE 0L
 #endif
 
@@ -23,6 +26,12 @@
 #ifdef DCFG_PTHREAD_SUPPORT
 #	include <pthread.h>
 #else
+#	ifdef __USE_POSIX199506
+#		undef __USE_POSIX199506
+#	endif
+#	ifdef __USE_UNIX98
+#		undef __USE_UNIX98
+#	endif
 typedef struct {
 	int unused;
 } pthread_mutex_t;