diff --git a/src/libexpr/flake/lockfile.cc b/src/libexpr/flake/lockfile.cc
index a34cfde97..b9caad92d 100644
--- a/src/libexpr/flake/lockfile.cc
+++ b/src/libexpr/flake/lockfile.cc
@@ -66,8 +66,10 @@ std::shared_ptr<Node> LockFile::findInput(const InputPath & path)
     return pos;
 }
 
-LockFile::LockFile(const nlohmann::json & json, std::string_view path)
+LockFile::LockFile(std::string_view contents, std::string_view path)
 {
+    auto json = nlohmann::json::parse(contents);
+
     auto version = json.value("version", 0);
     if (version < 5 || version > 7)
         throw Error("lock file '%s' has unsupported version %d", path, version);
@@ -116,11 +118,6 @@ LockFile::LockFile(const nlohmann::json & json, std::string_view path)
     // a bit since we don't need to worry about cycles.
 }
 
-LockFile::LockFile(std::string_view contents, std::string_view path)
-    : LockFile(nlohmann::json::parse(contents), path)
-{
-}
-
 nlohmann::json LockFile::toJSON() const
 {
     nlohmann::json nodes;
diff --git a/src/libexpr/flake/lockfile.hh b/src/libexpr/flake/lockfile.hh
index d51bdb86d..14210cfc9 100644
--- a/src/libexpr/flake/lockfile.hh
+++ b/src/libexpr/flake/lockfile.hh
@@ -50,7 +50,6 @@ struct LockFile
     std::shared_ptr<Node> root = std::make_shared<Node>();
 
     LockFile() {};
-    LockFile(const nlohmann::json & json, std::string_view path);
     LockFile(std::string_view contents, std::string_view path);
 
     nlohmann::json toJSON() const;