diff --git a/c/src/exec/score/cpu/unix/cpu.c b/c/src/exec/score/cpu/unix/cpu.c
index 428ae99c3b..a8fa6bb4d3 100644
--- a/c/src/exec/score/cpu/unix/cpu.c
+++ b/c/src/exec/score/cpu/unix/cpu.c
@@ -15,6 +15,7 @@
 #include <rtems/score/interr.h>
 
 #if defined(__linux__)
+#define _XOPEN_SOURCE
 #define MALLOC_0_RETURNS_NULL
 #endif
 
diff --git a/cpukit/score/cpu/unix/cpu.c b/cpukit/score/cpu/unix/cpu.c
index 428ae99c3b..a8fa6bb4d3 100644
--- a/cpukit/score/cpu/unix/cpu.c
+++ b/cpukit/score/cpu/unix/cpu.c
@@ -15,6 +15,7 @@
 #include <rtems/score/interr.h>
 
 #if defined(__linux__)
+#define _XOPEN_SOURCE
 #define MALLOC_0_RETURNS_NULL
 #endif