diff --git a/libgfortran/ChangeLog b/libgfortran/ChangeLog
index 84675b92ba5f..d2acafd09457 100644
--- a/libgfortran/ChangeLog
+++ b/libgfortran/ChangeLog
@@ -1,3 +1,8 @@
+2010-06-09  Francois-Xavier Coudert  <fxcoudert@gcc.gnu.org>
+
+	* intrinsics/system_clock.c (system_clock_4, system_clock_8):
+	Undefine TCK.
+
 2010-06-04  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
 	PR libfortran/34670
diff --git a/libgfortran/intrinsics/system_clock.c b/libgfortran/intrinsics/system_clock.c
index 7806059ccdf4..7cc82d0c8cd7 100644
--- a/libgfortran/intrinsics/system_clock.c
+++ b/libgfortran/intrinsics/system_clock.c
@@ -56,6 +56,7 @@ system_clock_4(GFC_INTEGER_4 *count, GFC_INTEGER_4 *count_rate,
   GFC_INTEGER_4 mx;
 
 #if defined(HAVE_SYS_TIME_H) && defined(HAVE_GETTIMEOFDAY)
+#undef TCK
 #define TCK 1000
   struct timeval tp1;
 
@@ -117,6 +118,7 @@ system_clock_8 (GFC_INTEGER_8 *count, GFC_INTEGER_8 *count_rate,
   GFC_INTEGER_8 mx;
 
 #if defined(HAVE_SYS_TIME_H) && defined(HAVE_GETTIMEOFDAY)
+#undef TCK
 #define TCK 1000000
   struct timeval tp1;