diff --git a/pkgs/by-name/li/libofx/c++20-allocate.patch b/pkgs/by-name/li/libofx/c++20-allocate.patch
new file mode 100644
index 000000000000..6be899da985e
--- /dev/null
+++ b/pkgs/by-name/li/libofx/c++20-allocate.patch
@@ -0,0 +1,79 @@
+From e326ba971fd40687d5e66fb2949e0d2f53e6d8fd Mon Sep 17 00:00:00 2001
+From: Ludovic Rousseau <ludovic.rousseau@free.fr>
+Date: Sat, 22 Aug 2026 15:46:10 +0200
+Subject: [PATCH] Use C++20 allocate()
+
+https://github.com/libofx/libofx/issues/105
+---
+ lib/tree.hh | 16 ++++++++--------
+ 1 file changed, 8 insertions(+), 8 deletions(-)
+
+diff --git a/lib/tree.hh b/lib/tree.hh
+index 3b42b28f..6bc62aa9 100644
+--- a/lib/tree.hh
++++ b/lib/tree.hh
+@@ -467,8 +467,8 @@ tree<T, tree_node_allocator>::~tree()
+ template <class T, class tree_node_allocator>
+ void tree<T, tree_node_allocator>::head_initialise_()
+ {
+-  head = alloc_.allocate(1, 0); // MSVC does not have default second argument
+-  feet = alloc_.allocate(1, 0);
++  head = alloc_.allocate(1);
++  feet = alloc_.allocate(1);
+ 
+   head->parent = 0;
+   head->first_child = 0;
+@@ -743,7 +743,7 @@ iter tree<T, tree_node_allocator>::append_child(iter position)
+ {
+   assert(position.node != head);
+ 
+-  tree_node* tmp = alloc_.allocate(1, 0);
++  tree_node* tmp = alloc_.allocate(1);
+   kp::constructor(&tmp->data);
+   tmp->first_child = 0;
+   tmp->last_child = 0;
+@@ -773,7 +773,7 @@ iter tree<T, tree_node_allocator>::append_child(iter position, const T& x)
+   // the API change.
+   assert(position.node != head);
+ 
+-  tree_node* tmp = alloc_.allocate(1, 0);
++  tree_node* tmp = alloc_.allocate(1);
+   kp::constructor(&tmp->data, x);
+   tmp->first_child = 0;
+   tmp->last_child = 0;
+@@ -833,7 +833,7 @@ iter tree<T, tree_node_allocator>::insert(iter position, const T& x)
+     position.node = feet; // Backward compatibility: when calling insert on a null node,
+     // insert before the feet.
+   }
+-  tree_node* tmp = alloc_.allocate(1, 0);
++  tree_node* tmp = alloc_.allocate(1);
+   kp::constructor(&tmp->data, x);
+   tmp->first_child = 0;
+   tmp->last_child = 0;
+@@ -856,7 +856,7 @@ iter tree<T, tree_node_allocator>::insert(iter position, const T& x)
+ template <class T, class tree_node_allocator>
+ typename tree<T, tree_node_allocator>::sibling_iterator tree<T, tree_node_allocator>::insert(sibling_iterator position, const T& x)
+ {
+-  tree_node* tmp = alloc_.allocate(1, 0);
++  tree_node* tmp = alloc_.allocate(1);
+   kp::constructor(&tmp->data, x);
+   tmp->first_child = 0;
+   tmp->last_child = 0;
+@@ -889,7 +889,7 @@ template <class T, class tree_node_allocator>
+ template <class iter>
+ iter tree<T, tree_node_allocator>::insert_after(iter position, const T& x)
+ {
+-  tree_node* tmp = alloc_.allocate(1, 0);
++  tree_node* tmp = alloc_.allocate(1);
+   kp::constructor(&tmp->data, x);
+   tmp->first_child = 0;
+   tmp->last_child = 0;
+@@ -951,7 +951,7 @@ iter tree<T, tree_node_allocator>::replace(iter position, const iterator_base& f
+ 
+   // replace the node at position with head of the replacement tree at from
+   erase_children(position);
+-  tree_node* tmp = alloc_.allocate(1, 0);
++  tree_node* tmp = alloc_.allocate(1);
+   kp::constructor(&tmp->data, (*from));
+   tmp->first_child = 0;
+   tmp->last_child = 0;
diff --git a/pkgs/by-name/li/libofx/package.nix b/pkgs/by-name/li/libofx/package.nix
index d74091756ecd..4774c6dafabf 100644
--- a/pkgs/by-name/li/libofx/package.nix
+++ b/pkgs/by-name/li/libofx/package.nix
@@ -24,6 +24,12 @@ stdenv.mkDerivation (finalAttrs: {
     sha256 = "sha256-KOQrEAt1jHrOpPQ7QbGUADe0i7sQXNH2fblPRzT0EIg=";
   };
 
+  # C++20 changes the signature of std::allocator::allocate. Vendored patch
+  # from the approved PR to fix this.
+  # https://github.com/libofx/libofx/issues/105
+  # https://github.com/libofx/libofx/pull/106
+  patches = [ ./c++20-allocate.patch ];
+
   preConfigure = "./autogen.sh";
   configureFlags = [ "--with-opensp-includes=${opensp}/include/OpenSP" ];
   nativeBuildInputs = [