diff --git a/src/Clock.ml b/src/Clock.ml
index d12f86d05d7c04cc833a8439660d3099e7682ebe..ccf93e4d248d1f41e9490e3df2e91a8fad1cc4c0 100644
--- a/src/Clock.ml
+++ b/src/Clock.ml
@@ -24,7 +24,7 @@ type clock = {
   mutable now: float;
   (* The number of ticks that have taken place. *)
   mutable ticks: int;
-  (* The last time [tick] was called for this clock. *)
+  (* The last time a user function [f] was called via [tick clock f]. *)
   mutable last: float;
   (* A circular array of the times at which the most recent round ticks
      took place. *)