diff --git a/refs.c b/refs.c
index 6c8fe18581f0ed92c71419a2940e83c966331a7b..ccbd04a0351d5810b2cc5b6b726e2f54cacdd3e8 100644
--- a/refs.c
+++ b/refs.c
@@ -529,6 +529,15 @@ static void sort_ref_dir(struct ref_dir *dir)
 /* Include broken references in a do_for_each_ref*() iteration: */
 #define DO_FOR_EACH_INCLUDE_BROKEN 0x01
 
+/*
+ * current_ref is a performance hack: when iterating over references
+ * using the for_each_ref*() functions, current_ref is set to the
+ * current reference's entry before calling the callback function.  If
+ * the callback function calls peel_ref(), then peel_ref() first
+ * checks whether the reference to be peeled is the current reference
+ * (it usually is) and if so, returns that reference's peeled version
+ * if it is available.  This avoids a refname lookup in a common case.
+ */
 static struct ref_entry *current_ref;
 
 /*