diff --git a/src/libexpr/primops/flake.cc b/src/libexpr/primops/flake.cc
index e1eeffca6..3c1cffba3 100644
--- a/src/libexpr/primops/flake.cc
+++ b/src/libexpr/primops/flake.cc
@@ -12,8 +12,7 @@
 
 namespace nix {
 
-/* Read the registry or a lock file. (Currently they have an identical
-   format. */
+/* Read a registry. */
 std::shared_ptr<FlakeRegistry> readRegistry(const Path & path)
 {
     auto registry = std::make_shared<FlakeRegistry>();
@@ -34,8 +33,8 @@ std::shared_ptr<FlakeRegistry> readRegistry(const Path & path)
     return registry;
 }
 
-/* Write the registry or lock file to a file. */
-void writeRegistry(FlakeRegistry registry, Path path)
+/* Write a registry to a file. */
+void writeRegistry(const FlakeRegistry & registry, Path path)
 {
     nlohmann::json json;
     json["version"] = 1;
diff --git a/src/libexpr/primops/flake.hh b/src/libexpr/primops/flake.hh
index 9da065234..8bfceb756 100644
--- a/src/libexpr/primops/flake.hh
+++ b/src/libexpr/primops/flake.hh
@@ -35,7 +35,7 @@ Value * makeFlakeValue(EvalState & state, const FlakeRef & flakeRef, bool impure
 
 std::shared_ptr<FlakeRegistry> readRegistry(const Path &);
 
-void writeRegistry(FlakeRegistry, Path);
+void writeRegistry(const FlakeRegistry &, Path);
 
 struct Flake
 {