diff --git a/src/regression/syscall-sign-extend.c b/src/regression/syscall-sign-extend.c
index 89ef9b6..7d3e0d8 100644
--- a/src/regression/syscall-sign-extend.c
+++ b/src/regression/syscall-sign-extend.c
@@ -16,8 +16,11 @@ static unsigned long long tsdiff(struct timespec ts2, struct timespec ts)
 		ts2.tv_nsec += 1000000000;
 		ts2.tv_sec--;
 	}
-	if (ts2.tv_sec < ts.tv_sec)
-		return -1;
+	if (ts2.tv_sec < ts.tv_sec) {
+		t_error("non-monotonic SYS_clock_gettime vs clock_gettime: %llu ns\n",
+			(ts.tv_sec - ts2.tv_sec)*1000000000ULL + ts.tv_nsec - ts2.tv_nsec);
+		return 0;
+	}
 	return (ts2.tv_sec - ts.tv_sec)*1000000000ULL + (ts2.tv_nsec - ts.tv_nsec);
 }
 
@@ -31,8 +34,10 @@ int main(void)
 
 	// check if timespec is filled correctly
 	T(clock_gettime(CLOCK_REALTIME, &ts2));
+	// adjust because linux vdso is non-monotonic wrt the syscall..
+	ts.tv_nsec += 2;
 	diff = tsdiff(ts2, ts);
-	if (diff > 10 * 1000000000ULL)
+	if (diff > 5 * 1000000000ULL)
 		t_error("large diff between clock_gettime calls: %llu ns\n", diff);
 
 	return t_status;