diff -r d5d6ab809ad3 -r deb0035635eb src/list.c
--- a/src/list.c	Wed May 09 20:15:10 2018 +0200
+++ b/src/list.c	Fri May 11 17:40:16 2018 +0200
@@ -142,6 +142,39 @@
     }
 }
 
+UcxList *ucx_list_prepend_once(UcxList *l, void *data,
+        cmp_func cmpfnc, void *cmpdata) {
+    return ucx_list_prepend_once_a(ucx_default_allocator(), l,
+            data, cmpfnc, cmpdata);
+}
+
+UcxList *ucx_list_prepend_once_a(UcxAllocator *alloc, UcxList *l, void *data,
+        cmp_func cmpfnc, void *cmpdata) {
+
+    UcxList* first = ucx_list_first(l);
+    {
+        UcxList *e = first;
+        while (e) {
+            if (cmpfnc(e->data, data, cmpdata) == 0) {
+                return l;
+            }
+            e = e->next;
+        }
+    }
+    
+    UcxList *nl = ucx_list_append_a(alloc, NULL, data);
+    if (!nl) {
+        return NULL;
+    }
+
+    if (first) {
+        nl->next = first;
+        first->prev = nl;
+    }
+    
+    return nl;
+}
+
 UcxList *ucx_list_prepend(UcxList *l, void *data) {
     return ucx_list_prepend_a(ucx_default_allocator(), l, data);
 }