diff --git a/pkgs/by-name/ld/ldb/package.nix b/pkgs/by-name/ld/ldb/package.nix
index 04d9e7d645bd..45e3f142befb 100644
--- a/pkgs/by-name/ld/ldb/package.nix
+++ b/pkgs/by-name/ld/ldb/package.nix
@@ -17,6 +17,7 @@
   buildPackages,
   libxcrypt,
   testers,
+  fetchpatch,
 }:
 
 stdenv.mkDerivation (finalAttrs: {
@@ -33,6 +34,16 @@ stdenv.mkDerivation (finalAttrs: {
     "dev"
   ];
 
+  patches = [
+    # Fix rep_memset_s calling C23 memset_explicit with wrong arg count (4 instead of 3).
+    # Upstream samba commit 04e0fb9b2d; later reworked more broadly in ef08be24e9 and 3e81b73a05
+    # which replace memset_s with memset_explicit entirely, but those don't apply to ldb 2.9.2.
+    (fetchpatch {
+      url = "https://gitlab.com/samba-team/samba/-/commit/04e0fb9b2d1d87516f1331096c78e8355b4fa9f3.patch";
+      hash = "sha256-sBqtVwGBXseCAMlv3QaiSYQmOw7H4cAJwc0Ey5yD6Os=";
+    })
+  ];
+
   nativeBuildInputs = [
     pkg-config
     python3