diff --git a/builder/default.nix b/builder/default.nix
index 42c95c7..9ae2845 100644
--- a/builder/default.nix
+++ b/builder/default.nix
@@ -161,6 +161,7 @@ let
 
   mkGoEnv =
     { pwd
+    , toolsGo ? pwd + "/tools.go"
     }@attrs:
     let
       goMod = parseGoMod (readFile "${toString pwd}/go.mod");
@@ -201,11 +202,11 @@ let
         export GOSUMDB=off
         export GOPROXY=off
 
-      '' + optionalString (pathExists (pwd + "/tools.go")) ''
+      '' + optionalString (pathExists toolsGo) ''
         mkdir source
         cp ${pwd + "/go.mod"} source/go.mod
         cp ${pwd + "/go.sum"} source/go.sum
-        cp ${pwd + "/tools.go"} source/tools.go
+        cp ${toolsGo} source/tools.go
         cd source
 
         rsync -a -K --ignore-errors ${vendorEnv}/ vendor
diff --git a/docs/nix-reference.md b/docs/nix-reference.md
index bb4317f..7e1a431 100644
--- a/docs/nix-reference.md
+++ b/docs/nix-reference.md
@@ -16,5 +16,6 @@ All other arguments are passed verbatim to `stdenv.mkDerivation`.
 ### mkGoEnv
 Arguments:
 - **pwd** Path to working directory.
+- **toolsGo** Path to `tools.go` (_default: `pwd + "/tools.go"`).
 
 All other arguments are passed verbatim to `stdenv.mkDerivation`.