diff --git a/src/libfetchers/fetchers.cc b/src/libfetchers/fetchers.cc
index 5cb0dac17..cce4193ea 100644
--- a/src/libfetchers/fetchers.cc
+++ b/src/libfetchers/fetchers.cc
@@ -144,13 +144,20 @@ std::pair<Tree, Input> Input::fetch(ref<Store> store) const
         .storePath = storePath,
     };
 
-    auto narHash = store->queryPathInfo(tree.storePath)->narHash;
+    checkLocked(*store, storePath, input);
+
+    return {std::move(tree), input};
+}
+
+void Input::checkLocked(Store & store, const StorePath & storePath, Input & input) const
+{
+    auto narHash = store.queryPathInfo(storePath)->narHash;
     input.attrs.insert_or_assign("narHash", narHash.to_string(SRI, true));
 
     if (auto prevNarHash = getNarHash()) {
         if (narHash != *prevNarHash)
             throw Error((unsigned int) 102, "NAR hash mismatch in input '%s' (%s), expected '%s', got '%s'",
-                to_string(), tree.actualPath, prevNarHash->to_string(SRI, true), narHash.to_string(SRI, true));
+                to_string(), store.printStorePath(storePath), prevNarHash->to_string(SRI, true), narHash.to_string(SRI, true));
     }
 
     if (auto prevLastModified = getLastModified()) {
@@ -168,8 +175,6 @@ std::pair<Tree, Input> Input::fetch(ref<Store> store) const
     input.locked = true;
 
     assert(input.hasAllInfo());
-
-    return {std::move(tree), input};
 }
 
 std::pair<ref<InputAccessor>, Input> Input::lazyFetch(ref<Store> store) const
@@ -328,6 +333,8 @@ std::pair<ref<InputAccessor>, Input> InputScheme::lazyFetch(ref<Store> store, co
 {
     auto [storePath, input2] = fetch(store, input);
 
+    input.checkLocked(*store, storePath, input2);
+
     return {makeFSInputAccessor(CanonPath(store->toRealPath(storePath))), input2};
 }
 
diff --git a/src/libfetchers/fetchers.hh b/src/libfetchers/fetchers.hh
index 6ca798b71..cc53e76b8 100644
--- a/src/libfetchers/fetchers.hh
+++ b/src/libfetchers/fetchers.hh
@@ -101,6 +101,10 @@ public:
     std::optional<Hash> getRev() const;
     std::optional<uint64_t> getRevCount() const;
     std::optional<time_t> getLastModified() const;
+
+private:
+
+    void checkLocked(Store & store, const StorePath & storePath, Input & input) const;
 };
 
 /* The InputScheme represents a type of fetcher.  Each fetcher
diff --git a/src/libfetchers/tarball.cc b/src/libfetchers/tarball.cc
index 6c551bd93..9489b9ca9 100644
--- a/src/libfetchers/tarball.cc
+++ b/src/libfetchers/tarball.cc
@@ -223,7 +223,8 @@ struct CurlInputScheme : InputScheme
     ParsedURL toURL(const Input & input) override
     {
         auto url = parseURL(getStrAttr(input.attrs, "url"));
-        // NAR hashes are preferred over file hashes since tar/zip files        // don't have a canonical representation.
+        // NAR hashes are preferred over file hashes since tar/zip
+        // files don't have a canonical representation.
         if (auto narHash = input.getNarHash())
             url.query.insert_or_assign("narHash", narHash->to_string(SRI, true));
         return url;