From bf959d33312809ad956ff73309dc78d82fcfc160 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=C3=A9clairevoyant?=
 <848000+eclairevoyant@users.noreply.github.com>
Date: Fri, 26 Jun 2026 21:46:31 -0400
Subject: [PATCH] python3Packages.afdko: fix build on darwin

---
 ...mtx-avoid-unsigned-integer-underflow.patch | 34 +++++++++++++++++++
 .../python-modules/afdko/default.nix          |  4 +++
 2 files changed, 38 insertions(+)
 create mode 100644 pkgs/development/python-modules/afdko/0001-addfeatures-hmtx-avoid-unsigned-integer-underflow.patch

diff --git a/pkgs/development/python-modules/afdko/0001-addfeatures-hmtx-avoid-unsigned-integer-underflow.patch b/pkgs/development/python-modules/afdko/0001-addfeatures-hmtx-avoid-unsigned-integer-underflow.patch
new file mode 100644
index 000000000000..eb4a03e68647
--- /dev/null
+++ b/pkgs/development/python-modules/afdko/0001-addfeatures-hmtx-avoid-unsigned-integer-underflow.patch
@@ -0,0 +1,34 @@
+From 91833ab6c1a769f82f30dbf126362d079905bfc6 Mon Sep 17 00:00:00 2001
+From: =?UTF-8?q?=C3=A9clairevoyant?=
+ <848000+eclairevoyant@users.noreply.github.com>
+Date: Fri, 26 Jun 2026 21:28:41 -0400
+Subject: [PATCH] addfeatures/hmtx: avoid unsigned integer underflow
+
+---
+ c/addfeatures/hotconv/hmtx.cpp | 8 ++++----
+ 1 file changed, 4 insertions(+), 4 deletions(-)
+
+diff --git a/c/addfeatures/hotconv/hmtx.cpp b/c/addfeatures/hotconv/hmtx.cpp
+index 9336c986..2d8ca98e 100644
+--- a/c/addfeatures/hotconv/hmtx.cpp
++++ b/c/addfeatures/hotconv/hmtx.cpp
+@@ -52,12 +52,12 @@ int hmtxFill(hotCtx g) {
+     /* Optimize metrics */
+     FWord width = hmtx.advanceWidth.back();
+     size_t i;
+-    for (i = hmtx.advanceWidth.size() - 2; i >= 0; i--) {
+-        if (hmtx.advanceWidth[i] != width)
++    for (i = hmtx.advanceWidth.size(); i >= 2; i--) {
++        if (hmtx.advanceWidth[i-2] != width)
+             break;
+     }
+-    if (i + 2 != hmtx.advanceWidth.size())
+-        hmtx.advanceWidth.resize(i+2);
++    if (i != hmtx.advanceWidth.size())
++        hmtx.advanceWidth.resize(i);
+ 
+     return hmtx.Fill();
+ }
+-- 
+2.54.0
+
diff --git a/pkgs/development/python-modules/afdko/default.nix b/pkgs/development/python-modules/afdko/default.nix
index 1053d44c328f..70eb28a87de0 100644
--- a/pkgs/development/python-modules/afdko/default.nix
+++ b/pkgs/development/python-modules/afdko/default.nix
@@ -69,6 +69,10 @@ buildPythonPackage (finalAttrs: {
 
     # Use antlr4 runtime from nixpkgs and link it dynamically
     ./use-dynamic-system-antlr4-runtime.patch
+
+    # integer underflow causes incorrect behavior
+    # patch submitted upstream as https://github.com/adobe-type-tools/afdko/pull/1843
+    ./0001-addfeatures-hmtx-avoid-unsigned-integer-underflow.patch
   ];
 
   env = {