diff --git a/pkgs/development/compilers/llvm/10/compiler-rt.nix b/pkgs/development/compilers/llvm/10/compiler-rt.nix
index 4d31229d64c4..c0ea436ae275 100644
--- a/pkgs/development/compilers/llvm/10/compiler-rt.nix
+++ b/pkgs/development/compilers/llvm/10/compiler-rt.nix
@@ -55,7 +55,10 @@ stdenv.mkDerivation rec {
   # can build this. If we didn't do it, basically the entire nixpkgs on Darwin would have an unfree dependency and we'd
   # get no binary cache for the entire platform. If you really find yourself wanting the TSAN, make this controllable by
   # a flag and turn the flag off during the stdenv build.
-  postPatch = stdenv.lib.optionalString stdenv.isDarwin ''
+  postPatch = ''
+    substituteInPlace cmake/builtin-config-ix.cmake \
+      --replace 'set(X86 i386)' 'set(X86 i386 i486 i586 i686)'
+  '' + stdenv.lib.optionalString stdenv.isDarwin ''
     substituteInPlace cmake/config-ix.cmake \
       --replace 'set(COMPILER_RT_HAS_TSAN TRUE)' 'set(COMPILER_RT_HAS_TSAN FALSE)'
   '' + stdenv.lib.optionalString (useLLVM) ''
diff --git a/pkgs/development/compilers/llvm/6/compiler-rt.nix b/pkgs/development/compilers/llvm/6/compiler-rt.nix
index 1bdba107d7dd..abb6796e3c78 100644
--- a/pkgs/development/compilers/llvm/6/compiler-rt.nix
+++ b/pkgs/development/compilers/llvm/6/compiler-rt.nix
@@ -54,7 +54,10 @@ stdenv.mkDerivation {
   # can build this. If we didn't do it, basically the entire nixpkgs on Darwin would have an unfree dependency and we'd
   # get no binary cache for the entire platform. If you really find yourself wanting the TSAN, make this controllable by
   # a flag and turn the flag off during the stdenv build.
-  postPatch = stdenv.lib.optionalString stdenv.isDarwin ''
+  postPatch = ''
+    substituteInPlace cmake/builtin-config-ix.cmake \
+      --replace 'set(X86 i386)' 'set(X86 i386 i486 i586 i686)'
+  '' + stdenv.lib.optionalString stdenv.isDarwin ''
     substituteInPlace cmake/config-ix.cmake \
       --replace 'set(COMPILER_RT_HAS_TSAN TRUE)' 'set(COMPILER_RT_HAS_TSAN FALSE)'
   '' + stdenv.lib.optionalString (useLLVM) ''
diff --git a/pkgs/development/compilers/llvm/7/compiler-rt.nix b/pkgs/development/compilers/llvm/7/compiler-rt.nix
index 055fb01215f0..e83a4a3c26f8 100644
--- a/pkgs/development/compilers/llvm/7/compiler-rt.nix
+++ b/pkgs/development/compilers/llvm/7/compiler-rt.nix
@@ -55,7 +55,10 @@ stdenv.mkDerivation {
   # can build this. If we didn't do it, basically the entire nixpkgs on Darwin would have an unfree dependency and we'd
   # get no binary cache for the entire platform. If you really find yourself wanting the TSAN, make this controllable by
   # a flag and turn the flag off during the stdenv build.
-  postPatch = stdenv.lib.optionalString stdenv.isDarwin ''
+  postPatch = ''
+    substituteInPlace cmake/builtin-config-ix.cmake \
+      --replace 'set(X86 i386)' 'set(X86 i386 i486 i586 i686)'
+  '' + stdenv.lib.optionalString stdenv.isDarwin ''
     substituteInPlace cmake/config-ix.cmake \
       --replace 'set(COMPILER_RT_HAS_TSAN TRUE)' 'set(COMPILER_RT_HAS_TSAN FALSE)'
   '' + stdenv.lib.optionalString (useLLVM) ''
diff --git a/pkgs/development/compilers/llvm/8/compiler-rt.nix b/pkgs/development/compilers/llvm/8/compiler-rt.nix
index 573c198d6dac..b11659a78cc5 100644
--- a/pkgs/development/compilers/llvm/8/compiler-rt.nix
+++ b/pkgs/development/compilers/llvm/8/compiler-rt.nix
@@ -55,7 +55,10 @@ stdenv.mkDerivation {
   # can build this. If we didn't do it, basically the entire nixpkgs on Darwin would have an unfree dependency and we'd
   # get no binary cache for the entire platform. If you really find yourself wanting the TSAN, make this controllable by
   # a flag and turn the flag off during the stdenv build.
-  postPatch = stdenv.lib.optionalString stdenv.isDarwin ''
+  postPatch = ''
+    substituteInPlace cmake/builtin-config-ix.cmake \
+      --replace 'set(X86 i386)' 'set(X86 i386 i486 i586 i686)'
+  '' + stdenv.lib.optionalString stdenv.isDarwin ''
     substituteInPlace cmake/config-ix.cmake \
       --replace 'set(COMPILER_RT_HAS_TSAN TRUE)' 'set(COMPILER_RT_HAS_TSAN FALSE)'
   '' + stdenv.lib.optionalString (useLLVM) ''
diff --git a/pkgs/development/compilers/llvm/9/compiler-rt.nix b/pkgs/development/compilers/llvm/9/compiler-rt.nix
index c7723a982914..7d712017eae9 100644
--- a/pkgs/development/compilers/llvm/9/compiler-rt.nix
+++ b/pkgs/development/compilers/llvm/9/compiler-rt.nix
@@ -54,7 +54,10 @@ stdenv.mkDerivation rec {
   # can build this. If we didn't do it, basically the entire nixpkgs on Darwin would have an unfree dependency and we'd
   # get no binary cache for the entire platform. If you really find yourself wanting the TSAN, make this controllable by
   # a flag and turn the flag off during the stdenv build.
-  postPatch = stdenv.lib.optionalString stdenv.isDarwin ''
+  postPatch = ''
+    substituteInPlace cmake/builtin-config-ix.cmake \
+      --replace 'set(X86 i386)' 'set(X86 i386 i486 i586 i686)'
+  '' + stdenv.lib.optionalString stdenv.isDarwin ''
     substituteInPlace cmake/config-ix.cmake \
       --replace 'set(COMPILER_RT_HAS_TSAN TRUE)' 'set(COMPILER_RT_HAS_TSAN FALSE)'
   '' + stdenv.lib.optionalString (useLLVM) ''