diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index 099cf4c58..59728e38d 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -478,7 +478,7 @@ LockedFlake lockFlake(
                             lockFlags.useRegistries, flakeCache);
 
                         newLocks.inputs.insert_or_assign(id,
-                            LockedInput(inputFlake.resolvedRef, inputFlake.originalRef, inputFlake.sourceInfo->info.narHash));
+                            LockedInput(inputFlake.resolvedRef, inputFlake.originalRef, inputFlake.sourceInfo->info));
 
                         /* Recursively process the inputs of this
                            flake. Also, unless we already have this
@@ -497,7 +497,7 @@ LockedFlake lockFlake(
                         auto [sourceInfo, resolvedRef] = getNonFlake(state, input.ref,
                             lockFlags.useRegistries, flakeCache);
                         newLocks.inputs.insert_or_assign(id,
-                            LockedInput(resolvedRef, input.ref, sourceInfo.info.narHash));
+                            LockedInput(resolvedRef, input.ref, sourceInfo.info));
                     }
                 }
             }
@@ -604,9 +604,14 @@ static void prim_callFlake(EvalState & state, const Pos & pos, Value * * args, V
     if (lazyInput->isFlake) {
         auto flake = getFlake(state, lazyInput->lockedInput.ref, false);
 
-        if (flake.sourceInfo->info.narHash != lazyInput->lockedInput.narHash)
-            throw Error("the content hash of flake '%s' doesn't match the hash recorded in the referring lockfile",
-                lazyInput->lockedInput.ref);
+        if (flake.sourceInfo->info.narHash != lazyInput->lockedInput.info.narHash)
+            throw Error("the content hash of flake '%s' (%s) doesn't match the hash recorded in the referring lock file (%s)",
+                lazyInput->lockedInput.ref,
+                flake.sourceInfo->info.narHash.to_string(SRI),
+                lazyInput->lockedInput.info.narHash.to_string(SRI));
+
+        // FIXME: check all the other attributes in lockedInput.info
+        // once we've dropped support for lock file version 4.
 
         assert(flake.sourceInfo->storePath == lazyInput->lockedInput.computeStorePath(*state.store));
 
@@ -615,9 +620,14 @@ static void prim_callFlake(EvalState & state, const Pos & pos, Value * * args, V
         FlakeCache flakeCache;
         auto [sourceInfo, resolvedRef] = getNonFlake(state, lazyInput->lockedInput.ref, false, flakeCache);
 
-        if (sourceInfo.info.narHash != lazyInput->lockedInput.narHash)
-            throw Error("the content hash of repository '%s' doesn't match the hash recorded in the referring lockfile",
-                lazyInput->lockedInput.ref);
+        if (sourceInfo.info.narHash != lazyInput->lockedInput.info.narHash)
+            throw Error("the content hash of repository '%s' (%s) doesn't match the hash recorded in the referring lock file (%s)",
+                lazyInput->lockedInput.ref,
+                sourceInfo.info.narHash.to_string(SRI),
+                lazyInput->lockedInput.info.narHash.to_string(SRI));
+
+        // FIXME: check all the other attributes in lockedInput.info
+        // once we've dropped support for lock file version 4.
 
         assert(sourceInfo.storePath == lazyInput->lockedInput.computeStorePath(*state.store));
 
diff --git a/src/libexpr/flake/lockfile.cc b/src/libexpr/flake/lockfile.cc
index 60fb914f9..6773b2844 100644
--- a/src/libexpr/flake/lockfile.cc
+++ b/src/libexpr/flake/lockfile.cc
@@ -44,28 +44,81 @@ FlakeRef getFlakeRef(
     throw Error("attribute '%s' missing in lock file", version4Attr);
 }
 
+static TreeInfo parseTreeInfo(const nlohmann::json & json)
+{
+    TreeInfo info;
+
+    auto i = json.find("info");
+    if (i != json.end()) {
+        const nlohmann::json & i2(*i);
+
+        auto j = i2.find("narHash");
+        if (j != i2.end())
+            info.narHash = Hash((std::string) *j);
+        else
+            throw Error("attribute 'narHash' missing in lock file");
+
+        j = i2.find("rev");
+        if (j != i2.end())
+            info.rev = Hash((std::string) *j, htSHA1);
+
+        j = i2.find("revCount");
+        if (j != i2.end())
+            info.revCount = *j;
+
+        j = i2.find("lastModified");
+        if (j != i2.end())
+            info.lastModified = *j;
+
+        return info;
+    }
+
+    i = json.find("narHash");
+    if (i != json.end()) {
+        info.narHash = Hash((std::string) *i);
+        return info;
+    }
+
+    throw Error("attribute 'info' missing in lock file");
+}
+
 LockedInput::LockedInput(const nlohmann::json & json)
     : LockedInputs(json)
     , ref(getFlakeRef(json, "url", "uri", "resolvedRef"))
     , originalRef(getFlakeRef(json, "originalUrl", "originalUri", "originalRef"))
-    , narHash(Hash((std::string) json["narHash"]))
+    , info(parseTreeInfo(json))
 {
     if (!ref.isImmutable())
         throw Error("lockfile contains mutable flakeref '%s'", ref);
 }
 
+static nlohmann::json treeInfoToJson(const TreeInfo & info)
+{
+    nlohmann::json json;
+    assert(info.narHash);
+    json["narHash"] = info.narHash.to_string(SRI);
+    if (info.rev)
+        json["rev"] = info.rev->gitRev();
+    if (info.revCount)
+        json["revCount"] = *info.revCount;
+    if (info.lastModified)
+        json["lastModified"] = *info.lastModified;
+    return json;
+}
+
 nlohmann::json LockedInput::toJson() const
 {
     auto json = LockedInputs::toJson();
     json["originalRef"] = fetchers::attrsToJson(originalRef.toAttrs());
     json["resolvedRef"] = fetchers::attrsToJson(ref.toAttrs());
-    json["narHash"] = narHash.to_string(SRI); // FIXME
+    json["info"] = treeInfoToJson(info);
     return json;
 }
 
 StorePath LockedInput::computeStorePath(Store & store) const
 {
-    return store.makeFixedOutputPath(true, narHash, "source");
+    assert(info.narHash);
+    return store.makeFixedOutputPath(true, info.narHash, "source");
 }
 
 LockedInputs::LockedInputs(const nlohmann::json & json)
diff --git a/src/libexpr/flake/lockfile.hh b/src/libexpr/flake/lockfile.hh
index a9710524b..d1cbf7c06 100644
--- a/src/libexpr/flake/lockfile.hh
+++ b/src/libexpr/flake/lockfile.hh
@@ -36,10 +36,10 @@ struct LockedInputs
 struct LockedInput : LockedInputs
 {
     FlakeRef ref, originalRef;
-    Hash narHash;
+    TreeInfo info;
 
-    LockedInput(const FlakeRef & ref, const FlakeRef & originalRef, const Hash & narHash)
-        : ref(ref), originalRef(originalRef), narHash(narHash)
+    LockedInput(const FlakeRef & ref, const FlakeRef & originalRef, const TreeInfo & info)
+        : ref(ref), originalRef(originalRef), info(info)
     { }
 
     LockedInput(const nlohmann::json & json);
@@ -48,7 +48,8 @@ struct LockedInput : LockedInputs
     {
         return
             ref == other.ref
-            && narHash == other.narHash
+            && originalRef == other.originalRef
+            && info == other.info
             && inputs == other.inputs;
     }
 
diff --git a/src/libstore/fetchers/tree-info.hh b/src/libstore/fetchers/tree-info.hh
index 30d4f3d6b..61500facb 100644
--- a/src/libstore/fetchers/tree-info.hh
+++ b/src/libstore/fetchers/tree-info.hh
@@ -5,9 +5,18 @@ namespace nix {
 struct TreeInfo
 {
     Hash narHash;
-    std::optional<Hash> rev;
+    std::optional<Hash> rev; // FIXME: remove
     std::optional<uint64_t> revCount;
     std::optional<time_t> lastModified;
+
+    bool operator ==(const TreeInfo & other) const
+    {
+        return
+            narHash == other.narHash
+            && rev == other.rev
+            && revCount == other.revCount
+            && lastModified == other.lastModified;
+    }
 };
 
 }