diff --git a/libraries/liblutil/csn.c b/libraries/liblutil/csn.c
index 4c3213f741..4eb29bcce2 100644
--- a/libraries/liblutil/csn.c
+++ b/libraries/liblutil/csn.c
@@ -48,6 +48,7 @@
 
 #include <lutil.h>
 
+/* Must be mutex-protected, because lutil_gettime needs mutex protection */
 size_t
 lutil_csnstr(char *buf, size_t len, unsigned int replica, unsigned int mod)
 {
diff --git a/libraries/liblutil/utils.c b/libraries/liblutil/utils.c
index 3891cfacf1..2cd105ed92 100644
--- a/libraries/liblutil/utils.c
+++ b/libraries/liblutil/utils.c
@@ -272,7 +272,9 @@ int lutil_parsetime( char *atm, struct lutil_tm *tm )
 	return -1;
 }
 
-/* return a broken out time, with microseconds */
+/* return a broken out time, with microseconds
+ * Must be mutex-protected.
+ */
 #ifdef _WIN32
 /* Windows SYSTEMTIME only has 10 millisecond resolution, so we
  * also need to use a high resolution timer to get microseconds.