diff --git a/pkgs/esp-idf/default.nix b/pkgs/esp-idf/default.nix
index 8856d17..62c2671 100644
--- a/pkgs/esp-idf/default.nix
+++ b/pkgs/esp-idf/default.nix
@@ -102,6 +102,8 @@ let
     pname = "esp-idf";
     version = rev;
 
+    preferLocalBuild = true;
+
     inherit src;
 
     # This is so that downstream derivations will have IDF_PATH set.
diff --git a/pkgs/esp-idf/tools.nix b/pkgs/esp-idf/tools.nix
index 80e665f..285a684 100644
--- a/pkgs/esp-idf/tools.nix
+++ b/pkgs/esp-idf/tools.nix
@@ -98,6 +98,9 @@ let
         inherit url sha256;
       };
 
+      # These are pre-built binary tarballs — no compilation happens, just download + autoPatchelf
+      preferLocalBuild = true;
+
       nativeBuildInputs = [ makeWrapper ] ++ lib.optionals stdenv.isLinux [ autoPatchelfHook ];
       buildInputs = lib.optionals stdenv.isLinux runtimeDeps;