diff -r e3bb67b72d33 -r 68ff0839bc6a src/cx/list.h
--- a/src/cx/list.h	Mon Jan 27 20:27:39 2025 +0100
+++ b/src/cx/list.h	Tue Jan 28 18:27:46 2025 +0100
@@ -362,6 +362,7 @@
         CxList *list,
         const void *elem
 ) {
+    list->collection.sorted = false;
     return list->cl->insert_element(list, list->collection.size, elem);
 }
 
@@ -387,6 +388,7 @@
         const void *array,
         size_t n
 ) {
+    list->collection.sorted = false;
     return list->cl->insert_array(list, list->collection.size, array, n);
 }
 
@@ -409,12 +411,15 @@
         size_t index,
         const void *elem
 ) {
+    list->collection.sorted = false;
     return list->cl->insert_element(list, index, elem);
 }
 
 /**
  * Inserts an item into a sorted list.
  *
+ * If the list is not sorted already, the behavior is undefined.
+ *
  * @param list the list
  * @param elem a pointer to the element to add
  * @retval zero success
@@ -425,6 +430,7 @@
         CxList *list,
         const void *elem
 ) {
+    list->collection.sorted = true; // guaranteed by definition
     const void *data = list->collection.store_pointer ? &elem : elem;
     return list->cl->insert_sorted(list, data, 1) == 0;
 }
@@ -455,6 +461,7 @@
         const void *array,
         size_t n
 ) {
+    list->collection.sorted = false;
     return list->cl->insert_array(list, index, array, n);
 }
 
@@ -470,6 +477,8 @@
  * If this list is storing pointers instead of objects @p array is expected to
  * be an array of pointers.
  *
+ * If the list is not sorted already, the behavior is undefined.
+ *
  * @param list the list
  * @param array a pointer to the elements to add
  * @param n the number of elements to add
@@ -481,6 +490,7 @@
         const void *array,
         size_t n
 ) {
+    list->collection.sorted = true; // guaranteed by definition
     return list->cl->insert_sorted(list, array, n);
 }
 
@@ -505,7 +515,9 @@
         CxIterator *iter,
         const void *elem
 ) {
-    return ((struct cx_list_s *) iter->src_handle.m)->cl->insert_iter(iter, elem, 0);
+    CxList* list = iter->src_handle.m;
+    list->collection.sorted = false;
+    return list->cl->insert_iter(iter, elem, 0);
 }
 
 /**
@@ -529,7 +541,9 @@
         CxIterator *iter,
         const void *elem
 ) {
-    return ((struct cx_list_s *) iter->src_handle.m)->cl->insert_iter(iter, elem, 1);
+    CxList* list = iter->src_handle.m;
+    list->collection.sorted = false;
+    return list->cl->insert_iter(iter, elem, 1);
 }
 
 /**
@@ -630,6 +644,7 @@
  */
 cx_attr_nonnull
 static inline void cxListClear(CxList *list) {
+    list->collection.sorted = true; // empty lists are always sorted
     list->cl->clear(list);
 }
 
@@ -652,6 +667,7 @@
         size_t i,
         size_t j
 ) {
+    list->collection.sorted = false;
     return list->cl->swap(list, i, j);
 }
 
@@ -874,6 +890,7 @@
 cx_attr_nonnull
 static inline void cxListSort(CxList *list) {
     list->cl->sort(list);
+    list->collection.sorted = true;
 }
 
 /**
@@ -883,6 +900,8 @@
  */
 cx_attr_nonnull
 static inline void cxListReverse(CxList *list) {
+    // still sorted, but not according to the cmp_func
+    list->collection.sorted = false;
     list->cl->reverse(list);
 }