diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index a30637262..4fa125f1b 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -530,7 +530,7 @@ LockedFlake lockFlake(
                         auto [sourceInfo, lockedRef] = fetchOrSubstituteTree(
                             state, input.ref, {}, lockFlags.useRegistries, flakeCache);
                         newLocks.inputs.insert_or_assign(id,
-                            LockedInput(lockedRef, input.ref, sourceInfo.info));
+                            LockedInput(lockedRef, input.ref, sourceInfo.info, false));
                     }
                 }
             }
diff --git a/src/libexpr/flake/lockfile.cc b/src/libexpr/flake/lockfile.cc
index bf55b4e3b..0a1795a16 100644
--- a/src/libexpr/flake/lockfile.cc
+++ b/src/libexpr/flake/lockfile.cc
@@ -72,6 +72,7 @@ LockedInput::LockedInput(const nlohmann::json & json)
     , lockedRef(getFlakeRef(json, "url", "uri", "locked"))
     , originalRef(getFlakeRef(json, "originalUrl", "originalUri", "original"))
     , info(parseTreeInfo(json))
+    , isFlake(json.find("flake") != json.end() ? (bool) json["flake"] : true)
 {
     if (!lockedRef.input->isImmutable())
         throw Error("lockfile contains mutable flakeref '%s'", lockedRef);
@@ -95,6 +96,7 @@ nlohmann::json LockedInput::toJson() const
     json["original"] = fetchers::attrsToJson(originalRef.toAttrs());
     json["locked"] = fetchers::attrsToJson(lockedRef.toAttrs());
     json["info"] = treeInfoToJson(info);
+    if (!isFlake) json["flake"] = false;
     return json;
 }
 
diff --git a/src/libexpr/flake/lockfile.hh b/src/libexpr/flake/lockfile.hh
index 6203c40cb..51649df3d 100644
--- a/src/libexpr/flake/lockfile.hh
+++ b/src/libexpr/flake/lockfile.hh
@@ -39,9 +39,14 @@ struct LockedInput : LockedInputs
 {
     FlakeRef lockedRef, originalRef;
     TreeInfo info;
+    bool isFlake = true;
 
-    LockedInput(const FlakeRef & lockedRef, const FlakeRef & originalRef, const TreeInfo & info)
-        : lockedRef(lockedRef), originalRef(originalRef), info(info)
+    LockedInput(
+        const FlakeRef & lockedRef,
+        const FlakeRef & originalRef,
+        const TreeInfo & info,
+        bool isFlake = true)
+        : lockedRef(lockedRef), originalRef(originalRef), info(info), isFlake(isFlake)
     { }
 
     LockedInput(const nlohmann::json & json);
@@ -52,7 +57,8 @@ struct LockedInput : LockedInputs
             lockedRef == other.lockedRef
             && originalRef == other.originalRef
             && info == other.info
-            && inputs == other.inputs;
+            && inputs == other.inputs
+            && isFlake == other.isFlake;
     }
 
     nlohmann::json toJson() const;