1 files changed, 4 insertions, 0 deletions

diff --git a/timer/include/timer.h b/timer/include/timer.h
index a8a3f8b..b65f8d4 100644
--- a/timer/include/timer.h
+++ b/timer/include/timer.h
@@ -6,6 +6,10 @@
 #ifdef _WIN32
 typedef uint64_t time_point;
 #else
+// 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.
+#define __USE_POSIX199309
 #include <time.h>
 typedef struct timespec time_point;
 #endif