Avoid macro redefinition.

1 files changed, 2 insertions, 0 deletions

diff --git a/timer/include/timer.h b/timer/include/timer.h
index b65f8d4..94781d6 100644
--- a/timer/include/timer.h
+++ b/timer/include/timer.h
@@ -9,7 +9,9 @@ typedef uint64_t time_point;
 // Need to macro to make CLOCK_REALTIME available when compiling with ISO C11.
 // The constant is only needed in the source file, but the header file needs to
 // include time.h too.
+#ifndef __USE_POSIX199309
 #define __USE_POSIX199309
+#endif //
 #include <time.h>
 typedef struct timespec time_point;
 #endif