diff --git a/lisp/emacs-lisp/igc.el b/lisp/emacs-lisp/igc.el
index c40fca57809..ceafa0f6ca0 100644
--- a/lisp/emacs-lisp/igc.el
+++ b/lisp/emacs-lisp/igc.el
@@ -491,6 +491,8 @@ This function is called from a timer;  see `igc-start-collecting-stats'."
 
 (defun igc--current-idle-time ()
   "Time since the last command finished, in seconds as a float.
+This calls `current-idle-time', then converts the return value
+to a float number of seconds.
 See `igc--on-idle'."
   (let ((idle-time (current-idle-time)))
     (if idle-time (float-time idle-time) 0)))
@@ -514,8 +516,8 @@ See `igc--on-idle'."
 
 (defun igc--on-idle (state repetition)
   "Timer function to do GC in idle Emacs state.
-Calls igc--arena-step, wrapper for mps_arena_step for this very purpose.
-See `igc-start-idle-timer."
+Calls `igc--arena-step', wrapper for mps_arena_step for this very purpose.
+See `igc-start-idle-timer'."
   (let ((timer2 (aref state 0)))
     (when timer2
       (cancel-timer timer2)))
diff --git a/src/igc.c b/src/igc.c
index c5f59da3418..1c462ba62f1 100644
--- a/src/igc.c
+++ b/src/igc.c
@@ -5795,12 +5795,12 @@ KEY is the key associated with DEPENDENCY in a hash table.  */)
 }
 
 DEFUN ("igc--arena-step", Figc__arena_step, Sigc__arena_step, 2, 2, 0,
-       doc: /* Do some GC work.
+       doc: /* Request some GC work while Emacs is idle.
 
 INTERVAL is the time, in seconds, that MPS is permitted to take.
 
-MULTIPLIER is the number of further similar calls that the client
-program expects to make during this idle period.
+MULTIPLIER is the number of further similar calls that Emacs
+expects to make during this idle period.
 
 Return t if there was work to do, nil otherwise. */)
   (Lisp_Object interval, Lisp_Object multiplier)