diff --git a/bsc/llvm-ompss2/clang-bad.nix b/bsc/llvm-ompss2/clang-bad.nix
new file mode 100644
index 0000000..114cb34
--- /dev/null
+++ b/bsc/llvm-ompss2/clang-bad.nix
@@ -0,0 +1,69 @@
+{
+  stdenv
+, fetchgit
+, cmake
+, lld
+, bash
+, python3
+, perl
+, clang
+, which
+, libelf
+, libffi
+, pkg-config
+, enableDebug ? false
+}:
+
+stdenv.mkDerivation rec {
+  version = "11.0.0";
+  pname = "clang-ompss2";
+  enableParallelBuilding = true;
+  isClang = true;
+  isClangWithOmpss = true;
+
+  buildInputs = [
+    which
+    clang
+    bash
+    python3
+    perl
+    cmake
+    lld
+    libelf
+    libffi
+    pkg-config
+  ];
+
+  hardeningDisable = [ "fortify" ];
+
+  cmakeBuildType = if enableDebug then "Debug" else "Release";
+
+  dontUseCmakeBuildDir = true;
+
+  preConfigure = ''
+    mkdir -p build
+    cd build
+  '';
+
+  cmakeDir="../llvm";
+  cmakeFlagsArray=[
+    "-DLLVM_ENABLE_LLD=ON"
+    "-DCMAKE_CXX_FLAGS_DEBUG=-g -ggnu-pubnames"
+    "-DCMAKE_EXE_LINKER_FLAGS_DEBUG=-Wl,-gdb-index"
+    "-DLLVM_LIT_ARGS=-sv --xunit-xml-output=xunit.xml"
+    "-DLLVM_ENABLE_PROJECTS=clang;openmp;compiler-rt"
+    "-DLLVM_INSTALL_TOOLCHAIN_ONLY=ON"
+    (if enableDebug then "-DLLVM_ENABLE_ASSERTIONS=ON" else "")
+  ];
+
+# About "-DCLANG_DEFAULT_NANOS6_HOME=${nanos6}", we could specify a default
+# nanos6 installation, but this is would require a recompilation of clang each
+# time nanos6 is changed. Better to use the environment variable NANOS6_HOME,
+# and specify nanos6 at run time.
+
+  src = builtins.fetchGit {
+    url = "ssh://git@bscpm02.bsc.es/llvm-ompss/llvm-mono.git";
+    rev = "e1c73c3691d2685a99d99e14c6110d2c880662c6";
+    ref = "master";
+  };
+}
diff --git a/bsc/llvm-ompss2/clang.nix b/bsc/llvm-ompss2/clang.nix
index 0e0f215..bc01b0a 100644
--- a/bsc/llvm-ompss2/clang.nix
+++ b/bsc/llvm-ompss2/clang.nix
@@ -41,7 +41,7 @@ stdenv.mkDerivation rec {
   cmakeBuildType = if enableDebug then "Debug" else "Release";
 
   dontUseCmakeBuildDir = true;
-  enableAssertions = "OFF";
+  enableAssertions = if enableDebug then "ON" else "OFF";
 
   preConfigure = ''
     mkdir -p build
diff --git a/default.nix b/default.nix
index 82c866c..683da82 100644
--- a/default.nix
+++ b/default.nix
@@ -92,6 +92,7 @@ let
 
     clang-ompss2-unwrapped = callPackage ./bsc/llvm-ompss2/clang.nix {
       stdenv = pkgs.llvmPackages_10.stdenv;
+      enableDebug = false;
     };
 
     clang-ompss2 = callPackage bsc/llvm-ompss2/default.nix {