diff --git a/pkgs/development/compilers/llvm/default.nix b/pkgs/development/compilers/llvm/default.nix
index bed6bf1fc13b..7ef7adfa324e 100644
--- a/pkgs/development/compilers/llvm/default.nix
+++ b/pkgs/development/compilers/llvm/default.nix
@@ -1,17 +1,21 @@
-{ stdenv, fetchurl, perl, groff, cmake, python, libffi, binutils_gold }:
+{ stdenv, fetchurl, perl, groff, cmake, python, libffi, binutils_gold, version }:
 
-let version = "3.3"; in
+with { inherit (stdenv.lib) optional; };
+
+assert version == "3.4" || version == "3.3";
 
 stdenv.mkDerivation rec {
   name = "llvm-${version}";
 
   src = fetchurl {
     url    = "http://llvm.org/releases/${version}/llvm-${version}.src.tar.gz";
-    sha256 = "0y3mfbb5qzcpw3v5qncn69x1hdrrrfirgs82ypi2annhf0g6nxk8";
+    sha256 =
+      if version == "3.4" then "0a169ba045r4apb9cv6ncrwl83l7yiajnzirkcdlhj1cd4nn3995"
+        else       /*3.3*/     "0y3mfbb5qzcpw3v5qncn69x1hdrrrfirgs82ypi2annhf0g6nxk8";
   };
 
   # The default rlimits are too low for shared libraries.
-  patches = [ ./more-memory-for-bugpoint.patch ];
+  patches = optional (version == "3.3") [ ./more-memory-for-bugpoint.patch ];
 
   # libffi was propagated before, but it wasn't even being used, so
   # unless something needs it just an input is fine.
@@ -25,8 +29,9 @@ stdenv.mkDerivation rec {
     "-DCMAKE_BUILD_TYPE=Release"
     "-DLLVM_ENABLE_FFI=ON"
     "-DLLVM_BINUTILS_INCDIR=${binutils_gold}/include"
-    "-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=R600" # for mesa
-  ] ++ lib.optional (!isDarwin) "-DBUILD_SHARED_LIBS=ON";
+  ]
+    ++ optional (version == "3.3") "-DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD=R600" # for mesa
+    ++ optional (!isDarwin) "-DBUILD_SHARED_LIBS=ON";
 
   enableParallelBuilding = true;
 
diff --git a/pkgs/top-level/all-packages.nix b/pkgs/top-level/all-packages.nix
index c7d86057fb4f..0a0ac731cd75 100644
--- a/pkgs/top-level/all-packages.nix
+++ b/pkgs/top-level/all-packages.nix
@@ -2903,11 +2903,14 @@ let
 
   lessc = callPackage ../development/compilers/lessc { };
 
-  llvm = callPackage ../development/compilers/llvm {
+  llvm = llvm_33; # deprecated, depend on llvm_* directly
+  llvm_34 = callPackage ../development/compilers/llvm {
+    version = "3.4";
     stdenv = if stdenv.isDarwin
       then stdenvAdapters.overrideGCC stdenv gccApple
       else stdenv;
   };
+  llvm_33 = llvm_34.override { version = "3.3"; };
 
   mentorToolchains = recurseIntoAttrs (
     callPackage_i686 ../development/compilers/mentor {}