diff --git a/pkgs/development/beam-modules/fetch-mix-deps.nix b/pkgs/development/beam-modules/fetch-mix-deps.nix
index efdaba4368c8..513e56291835 100644
--- a/pkgs/development/beam-modules/fetch-mix-deps.nix
+++ b/pkgs/development/beam-modules/fetch-mix-deps.nix
@@ -21,7 +21,7 @@ stdenvNoCC.mkDerivation ({
   configurePhase = ''
     mkdir -p $out/deps
     mkdir -p $out/.hex
-    export HEX_HOME="$out/.hex";
+    export HEX_HOME="$TEMPDIR/.hex";
     export MIX_HOME="$TEMPDIR/.mix";
     export MIX_DEPS_PATH="$out/deps";
   '';