diff --git a/doc/languages-frameworks/rust.section.md b/doc/languages-frameworks/rust.section.md
index 09de57ff2bed..70d31f4eab42 100644
--- a/doc/languages-frameworks/rust.section.md
+++ b/doc/languages-frameworks/rust.section.md
@@ -142,7 +142,7 @@ rustPlatform.buildRustPackage rec {
   version = "1.0.0";
 
   cargoLock = let
-    fixupLockFile = path: /* ... */;
+    fixupLockFile = path: f (builtins.readFile path);
   in {
     lockFileContents = fixupLockFile ./Cargo.lock;
   };