diff --git a/pkgs/development/compilers/llvm/4/llvm.nix b/pkgs/development/compilers/llvm/4/llvm.nix
index 8fed435e3ae83..2039e07904b7f 100644
--- a/pkgs/development/compilers/llvm/4/llvm.nix
+++ b/pkgs/development/compilers/llvm/4/llvm.nix
@@ -33,7 +33,7 @@ let
     let target = stdenv.targetPlatform;
     in     if target.isAarch64 then "AARCH64"
       else if target.isArm     then "ARM"
-      else if target.isx86_64  then "X86"
+      else if target.isx86     then "X86"
       else throw "unknown platform";
   cmakeBuildType = if debugVersion then "Debug" else "Release";
 
diff --git a/pkgs/development/compilers/llvm/5/llvm.nix b/pkgs/development/compilers/llvm/5/llvm.nix
index 382643f86e845..f33a611eb79fe 100644
--- a/pkgs/development/compilers/llvm/5/llvm.nix
+++ b/pkgs/development/compilers/llvm/5/llvm.nix
@@ -33,7 +33,7 @@ let
     let target = stdenv.targetPlatform;
     in     if target.isAarch64 then "AARCH64"
       else if target.isArm     then "ARM"
-      else if target.isx86_64  then "X86"
+      else if target.isx86     then "X86"
       else throw "unknown platform";
   cmakeBuildType = if debugVersion then "Debug" else "Release";