diff --git a/src/backend/lib/ilist.c b/src/backend/lib/ilist.c
index 8ea38095cd8..f06febd6985 100644
--- a/src/backend/lib/ilist.c
+++ b/src/backend/lib/ilist.c
@@ -28,7 +28,7 @@
  * Caution: this is O(n); consider using slist_delete_current() instead.
  */
 void
-slist_delete(slist_head *head, slist_node *node)
+slist_delete(slist_head *head, const slist_node *node)
 {
 	slist_node *last = &head->head;
 	slist_node *cur;
@@ -57,7 +57,7 @@ slist_delete(slist_head *head, slist_node *node)
  *		Validate that 'node' is a member of 'head'
  */
 void
-dlist_member_check(dlist_head *head, dlist_node *node)
+dlist_member_check(const dlist_head *head, const dlist_node *node)
 {
 	dlist_iter	iter;
 
@@ -73,7 +73,7 @@ dlist_member_check(dlist_head *head, dlist_node *node)
  * Verify integrity of a doubly linked list
  */
 void
-dlist_check(dlist_head *head)
+dlist_check(const dlist_head *head)
 {
 	dlist_node *cur;
 
@@ -110,7 +110,7 @@ dlist_check(dlist_head *head)
  * Verify integrity of a singly linked list
  */
 void
-slist_check(slist_head *head)
+slist_check(const slist_head *head)
 {
 	slist_node *cur;
 
diff --git a/src/include/lib/ilist.h b/src/include/lib/ilist.h
index 3a9209d1c10..d33048f3b38 100644
--- a/src/include/lib/ilist.h
+++ b/src/include/lib/ilist.h
@@ -286,12 +286,12 @@ typedef struct slist_mutable_iter
 /* Prototypes for functions too big to be inline */
 
 /* Caution: this is O(n); consider using slist_delete_current() instead */
-extern void slist_delete(slist_head *head, slist_node *node);
+extern void slist_delete(slist_head *head, const slist_node *node);
 
 #ifdef ILIST_DEBUG
-extern void dlist_member_check(dlist_head *head, dlist_node *node);
-extern void dlist_check(dlist_head *head);
-extern void slist_check(slist_head *head);
+extern void dlist_member_check(const dlist_head *head, const dlist_node *node);
+extern void dlist_check(const dlist_head *head);
+extern void slist_check(const slist_head *head);
 #else
 /*
  * These seemingly useless casts to void are here to keep the compiler quiet
@@ -322,7 +322,7 @@ dlist_init(dlist_head *head)
  * An empty list has either its first 'next' pointer set to NULL, or to itself.
  */
 static inline bool
-dlist_is_empty(dlist_head *head)
+dlist_is_empty(const dlist_head *head)
 {
 	dlist_check(head);
 
@@ -465,7 +465,7 @@ dlist_move_tail(dlist_head *head, dlist_node *node)
  * Caution: unreliable if 'node' is not in the list.
  */
 static inline bool
-dlist_has_next(dlist_head *head, dlist_node *node)
+dlist_has_next(const dlist_head *head, const dlist_node *node)
 {
 	return node->next != &head->head;
 }
@@ -475,7 +475,7 @@ dlist_has_next(dlist_head *head, dlist_node *node)
  * Caution: unreliable if 'node' is not in the list.
  */
 static inline bool
-dlist_has_prev(dlist_head *head, dlist_node *node)
+dlist_has_prev(const dlist_head *head, const dlist_node *node)
 {
 	return node->prev != &head->head;
 }
@@ -629,7 +629,7 @@ dclist_init(dclist_head *head)
  *		Returns true if the list is empty, otherwise false.
  */
 static inline bool
-dclist_is_empty(dclist_head *head)
+dclist_is_empty(const dclist_head *head)
 {
 	Assert(dlist_is_empty(&head->dlist) == (head->count == 0));
 	return (head->count == 0);
@@ -773,7 +773,7 @@ dclist_move_tail(dclist_head *head, dlist_node *node)
  * Caution: 'node' must be a member of 'head'.
  */
 static inline bool
-dclist_has_next(dclist_head *head, dlist_node *node)
+dclist_has_next(const dclist_head *head, const dlist_node *node)
 {
 	dlist_member_check(&head->dlist, node);
 	Assert(head->count > 0);
@@ -788,7 +788,7 @@ dclist_has_next(dclist_head *head, dlist_node *node)
  * Caution: 'node' must be a member of 'head'.
  */
 static inline bool
-dclist_has_prev(dclist_head *head, dlist_node *node)
+dclist_has_prev(const dclist_head *head, const dlist_node *node)
 {
 	dlist_member_check(&head->dlist, node);
 	Assert(head->count > 0);
@@ -866,7 +866,7 @@ dclist_tail_node(dclist_head *head)
  *		Returns the stored number of entries in 'head'
  */
 static inline uint32
-dclist_count(dclist_head *head)
+dclist_count(const dclist_head *head)
 {
 	Assert(dlist_is_empty(&head->dlist) == (head->count == 0));
 
@@ -929,7 +929,7 @@ slist_init(slist_head *head)
  * Is the list empty?
  */
 static inline bool
-slist_is_empty(slist_head *head)
+slist_is_empty(const slist_head *head)
 {
 	slist_check(head);
 
@@ -977,7 +977,7 @@ slist_pop_head_node(slist_head *head)
  * Check whether 'node' has a following node.
  */
 static inline bool
-slist_has_next(slist_head *head, slist_node *node)
+slist_has_next(const slist_head *head, const slist_node *node)
 {
 	slist_check(head);