diff --git a/pkgs/by-name/ca/casadi/clang-19.diff b/pkgs/by-name/ca/casadi/clang-19.diff
deleted file mode 100644
index e7706cb320ba..000000000000
--- a/pkgs/by-name/ca/casadi/clang-19.diff
+++ /dev/null
@@ -1,35 +0,0 @@
-diff --git a/casadi/interfaces/clang/clang_compiler.hpp b/casadi/interfaces/clang/clang_compiler.hpp
-index 7f54853..9f8d4b1 100644
---- a/casadi/interfaces/clang/clang_compiler.hpp
-+++ b/casadi/interfaces/clang/clang_compiler.hpp
-@@ -52,7 +52,7 @@
- #include "llvm/IR/LLVMContext.h"
- //#include "llvm/IR/Verifier.h"
- #include <llvm/Support/FileSystem.h>
--#include <llvm/Support/Host.h>
-+#include <llvm/TargetParser/Host.h>
- #include <llvm/Support/ManagedStatic.h>
- #include <llvm/Support/Path.h>
- #include <llvm/Support/TargetSelect.h>
-diff --git a/cmake/FindCLANG.cmake b/cmake/FindCLANG.cmake
-index 4edf60b..f23a348 100644
---- a/cmake/FindCLANG.cmake
-+++ b/cmake/FindCLANG.cmake
-@@ -16,7 +16,7 @@ set(CLANG_CXX_FLAGS "-fPIC -fvisibility-inlines-hidden -ffunction-sections -fdat
- set(CLANG_INCLUDE_DIR ${LLVM_INSTALL_PREFIX}/include)
- 
- # All clang libraries
--set(CLANG_DEP clangFrontend clangDriver clangCodeGen clangRewriteFrontend clangSerialization clangParse clangSema clangAnalysis clangEdit clangAST clangLex clangBasic ${LLVM_DEP})
-+set(CLANG_DEP clangFrontend clangDriver clangCodeGen clangRewriteFrontend clangSerialization clangParse clangSema clangAPINotes clangAnalysis clangEdit clangAST clangLex clangBasic ${LLVM_DEP})
- 
- # Get libraries
- set(CLANG_LIBRARIES)
-@@ -86,7 +86,7 @@ set(CLANG_INCLUDE_DIR ${CLANG_LLVM_INCLUDE_DIR})
- 
- # All clang libraries
- set(CLANG_DEP clangFrontend clangDriver clangCodeGen clangRewriteFrontend clangSerialization
--              clangParse clangSema clangAnalysis clangEdit clangAST clangLex clangBasic)
-+              clangParse clangSema clangAPINotes clangAnalysis clangEdit clangAST clangLex clangBasic)
- 
- # Get libraries
- foreach(D ${CLANG_DEP})
diff --git a/pkgs/by-name/ca/casadi/package.nix b/pkgs/by-name/ca/casadi/package.nix
index c2a247525efc..fbaf8cf27e3c 100644
--- a/pkgs/by-name/ca/casadi/package.nix
+++ b/pkgs/by-name/ca/casadi/package.nix
@@ -48,10 +48,6 @@ stdenv.mkDerivation (finalAttrs: {
   };
 
   patches = [
-    # update include file path and link with clangAPINotes
-    # https://github.com/casadi/casadi/issues/3969
-    ./clang-19.diff
-
     # Add missing include
     # ref. https://github.com/casadi/casadi/pull/4192
     (fetchpatch {
@@ -77,11 +73,6 @@ stdenv.mkDerivation (finalAttrs: {
       "FATROP HPIPM" \
       "FATROP hpipm"
 
-    # nix provide lib/clang headers in libclang, not in llvm.
-    substituteInPlace casadi/interfaces/clang/CMakeLists.txt --replace-fail \
-      '$'{CLANG_LLVM_LIB_DIR} \
-      ${lib.getLib llvmPackages.libclang}/lib
-
     # help casadi find its own libs
     substituteInPlace casadi/core/casadi_os.cpp --replace-fail \
       "std::vector<std::string> search_paths;" \
@@ -108,11 +99,6 @@ stdenv.mkDerivation (finalAttrs: {
     substituteInPlace casadi/interfaces/hpipm/hpipm_runtime.hpp --replace-fail \
       "d_print_exp_tran_mat" \
       "//d_print_exp_tran_mat"
-
-    # fix missing symbols
-    substituteInPlace cmake/FindCLANG.cmake --replace-fail \
-      "clangBasic)" \
-      "clangBasic clangASTMatchers clangSupport)"
   '';
 
   nativeBuildInputs = [
@@ -189,7 +175,9 @@ stdenv.mkDerivation (finalAttrs: {
     (lib.cmakeBool "WITH_TINYXML" true)
     (lib.cmakeBool "WITH_BUILD_DSDP" true) # not sure where this come from
     (lib.cmakeBool "WITH_DSDP" true)
-    (lib.cmakeBool "WITH_CLANG" true)
+    # "clang_compiler.cpp has basically been abandonded for several years", ref.
+    # https://github.com/casadi/casadi/issues/4225#issuecomment-3352552113
+    (lib.cmakeBool "WITH_CLANG" false) 
     (lib.cmakeBool "WITH_LAPACK" true)
     (lib.cmakeBool "WITH_QPOASES" true)
     (lib.cmakeBool "WITH_BLOCKSQP" true)