diff --git a/lib/metadata/lv_manip.c b/lib/metadata/lv_manip.c
index e41e3279b..008a2cf7e 100644
--- a/lib/metadata/lv_manip.c
+++ b/lib/metadata/lv_manip.c
@@ -929,7 +929,7 @@ static int _is_condition(struct cmd_context *cmd __attribute((unused)),
 		return 1;
 
 	/*
-	 * Only used for cling and contiguous policies so its safe to say all
+	 * Only used for cling and contiguous policies so it's safe to say all
 	 * the available space is used.
 	 */
 	pvmatch->areas[s].pva = pvmatch->pva;
diff --git a/lib/metadata/pv_map.h b/lib/metadata/pv_map.h
index 6d6cfff23..bc5919252 100644
--- a/lib/metadata/pv_map.h
+++ b/lib/metadata/pv_map.h
@@ -39,7 +39,9 @@ struct pv_area {
  * an allocation attempt, track the maximum number of extents that may
  * need to be used as a particular parallel area.  Several of these
  * structs may reference the same pv_area, but 'used' may differ between
- * them.
+ * them.  The sum of all the 'used' variables referring to the same
+ * pv_area may not exceed that area's count, so we cannot allocate the
+ * same extents twice.
  */
 struct pv_area_used {
 	struct pv_area *pva;