diff --git a/mps/code/lockli.c b/mps/code/lockli.c
index deac899e0f2..8bd03649bbf 100644
--- a/mps/code/lockli.c
+++ b/mps/code/lockli.c
@@ -22,15 +22,14 @@
  * while we hold the mutex. 
  */
 
-#define _XOPEN_SOURCE 500
-#include <pthread.h>
-#include <semaphore.h>
-#include <errno.h>
-
 #include "mpmtypes.h"
 #include "lock.h"
 #include "config.h"
 
+#include <pthread.h>
+#include <semaphore.h>
+#include <errno.h>
+
 
 #ifndef MPS_OS_LI
 #error "lockli.c is specific to LinuxThreads but MPS_OS_LI not defined"
diff --git a/mps/code/mpstd.h b/mps/code/mpstd.h
index 2f3f3f4d94b..a7b1783edc8 100644
--- a/mps/code/mpstd.h
+++ b/mps/code/mpstd.h
@@ -186,7 +186,9 @@
 #define MPS_WORD_SHIFT  5
 #define MPS_PF_ALIGN    4
 
-#define _REENTRANT        /* FIXME: What for? */
+#ifndef _REENTRANT        /* it's also defined by cc -pthread */
+#define _REENTRANT        /* defines, e.g., pthread_mutexattr_settype */
+#endif
 #define _XOPEN_SOURCE 500 /* to get POSIX signal handling */
 #define _GNU_SOURCE       /* to get register numbers for prmci3li.c */
 
@@ -208,7 +210,9 @@
 #define MPS_WORD_SHIFT  6
 #define MPS_PF_ALIGN    8
 
-#define _REENTRANT        /* FIXME: What for? */
+#ifndef _REENTRANT        /* it's also defined by cc -pthread */
+#define _REENTRANT        /* defines, e.g., pthread_mutexattr_settype */
+#endif
 #define _XOPEN_SOURCE 500 /* to get POSIX signal handling */
 #define _GNU_SOURCE       /* to get register numbers for prmci3li.c */
 
diff --git a/mps/code/protix.c b/mps/code/protix.c
index b121e2f48ae..31c272bc5b9 100644
--- a/mps/code/protix.c
+++ b/mps/code/protix.c
@@ -39,11 +39,6 @@
  *    is permitted when PROT_NONE alone is used.
  */
 
-
-/* open sesame magic, see standards(5) */
-#define _POSIX_C_SOURCE 199309L
-#define _XOPEN_SOURCE_EXTENDED 1
-
 #include "mpm.h"
 
 #if !defined(MPS_OS_LI) && !defined(MPS_OS_FR) && !defined(MPS_OS_XC)