diff --git a/src/backend/postmaster/syslogger.c b/src/backend/postmaster/syslogger.c
index 5434826..e58d6e6 100644
--- a/src/backend/postmaster/syslogger.c
+++ b/src/backend/postmaster/syslogger.c
@@ -1225,6 +1225,8 @@ logfile_rotate(bool time_based_rotation, int size_rotation_for)
 	 * different from what we were previously logging into.
 	 *
 	 * Note: last_file_name should never be NULL here, but if it is, append.
+	 * (last_file_name is NULL if logfile_getname() runs out of RAM on
+	 * syslogger startup.)
 	 */
 	rotate_stderr = time_based_rotation ||
 		(size_rotation_for & LOG_DESTINATION_STDERR);