diff --git a/src/libfetchers/mercurial.cc b/src/libfetchers/mercurial.cc
index dd31e224f..e35bd8c49 100644
--- a/src/libfetchers/mercurial.cc
+++ b/src/libfetchers/mercurial.cc
@@ -213,26 +213,24 @@ struct MercurialInputScheme : InputScheme
                     runHg({"status", "-R", actualUrl, "--clean", "--modified", "--added", "--no-status", "--print0"}),
                     "\0"s);
 
-                std::filesystem::path actualPath(absPath(actualUrl));
+                auto accessor = makeFSSourceAccessor(absPath(actualUrl));
 
                 PathFilter filter = [&](const Path & p) -> bool {
-                    assert(hasPrefix(p, actualPath.string()));
-                    std::string file(p, actualPath.string().size() + 1);
+                    auto cp = CanonPath(p);
+                    auto st = accessor->lstat(cp);
 
-                    auto st = lstat(p);
-
-                    if (S_ISDIR(st.st_mode)) {
-                        auto prefix = file + "/";
+                    if (st.type == SourceAccessor::tDirectory) {
+                        auto prefix = cp.rel() + "/";
                         auto i = files.lower_bound(prefix);
                         return i != files.end() && hasPrefix(*i, prefix);
                     }
 
-                    return files.count(file);
+                    return files.count(cp.rel());
                 };
 
                 auto storePath = store.addToStore(
                     input.getName(),
-                    {getFSSourceAccessor(), CanonPath(actualPath.string())},
+                    {accessor, CanonPath::root},
                     ContentAddressMethod::Raw::NixArchive,
                     HashAlgorithm::SHA256,
                     {},
@@ -334,7 +332,7 @@ struct MercurialInputScheme : InputScheme
 
         deletePath(tmpDir / ".hg_archival.txt");
 
-        auto storePath = store.addToStore(name, {getFSSourceAccessor(), CanonPath(tmpDir.string())});
+        auto storePath = store.addToStore(name, {makeFSSourceAccessor(tmpDir), CanonPath::root});
 
         Attrs infoAttrs({
             {"revCount", (uint64_t) revCount},