diff --git a/overlays.nix b/overlays.nix
index 1014210..9890c32 100755
--- a/overlays.nix
+++ b/overlays.nix
@@ -92,6 +92,55 @@ let
     }
   );
 
+  # https://github.com/NixOS/nixpkgs/pull/392938
+  # usage: nix-build ./dev.nix -A <package>.src.unpacked
+  overlays.withUnpacked = final: prev: {
+    fetchurl = (lib.mirrorFunctionArgs prev.fetchurl) (
+      args:
+      let
+        fetched = prev.fetchurl args;
+      in
+      fetched.overrideAttrs (old: {
+        passthru = {
+          unpacked =
+            if old.outputHashMode == "recursive" then
+              fetched
+            else
+              prev.srcOnly {
+                name = "${fetched.name}-unpacked";
+                src = fetched;
+                stdenv = prev.stdenvNoCC;
+                inherit (old) preferLocalBuild;
+              };
+        } // old.passthru or { };
+      })
+    );
+    fetchgit = (lib.mirrorFunctionArgs prev.fetchgit) (
+      args:
+      (prev.fetchgit args).overrideAttrs (old: {
+        passthru = {
+          unpacked = prev.fetchgit args;
+        } // old.passthru or { };
+      })
+    );
+    fetchhg = (lib.mirrorFunctionArgs prev.fetchhg) (
+      args:
+      (prev.fetchhg args).overrideAttrs (old: {
+        passthru = {
+          unpacked = prev.fetchhg args;
+        } // old.passthru or { };
+      })
+    );
+    fetchsvn = (lib.mirrorFunctionArgs prev.fetchsvn) (
+      args:
+      (prev.fetchsvn args).overrideAttrs (old: {
+        passthru = {
+          unpacked = prev.fetchsvn args;
+        } // old.passthru or { };
+      })
+    );
+  };
+
   # usage: nix-build ./dev.nix -A <package>.shellcheck
   overlays.withShellCheck = mkDerivationOverlay (
     final: prev: prevStdenv: finalAttrs: prevAttrs:
@@ -361,7 +410,7 @@ let
       mkPkgs =
         {
           config ? { },
-          # overlays ? [ ],
+        # overlays ? [ ],
         }:
         import prev.path {
           # if we don't specify overlays then impure.nix will do its thing
@@ -385,6 +434,7 @@ in
   overlays.withShellCheck
   overlays.withDebug
   overlays.withInvalidateFetcherByDrvHash
+  overlays.withUnpacked
   overlays.withTwostagePythonBuildPassthru
   overlays.withPytestCheckHooks
   overlays.toplevelCudaRocmPkgs