diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index f9abd8cbd..b61868413 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -231,14 +231,14 @@ ref<const ValidPathInfo> BinaryCacheStore::addToStoreCommon(
             std::regex regex1("^[0-9a-f]{2}$");
             std::regex regex2("^[0-9a-f]{38}\\.debug$");
 
-            for (auto & s1 : narAccessor->readDirectory(buildIdDir)) {
+            for (auto & [s1, _type] : narAccessor->readDirectory(buildIdDir)) {
                 auto dir = buildIdDir + "/" + s1;
 
                 if (auto st = narAccessor->stat(dir); !st || st->type != SourceAccessor::tDirectory
                     || !std::regex_match(s1, regex1))
                     continue;
 
-                for (auto & s2 : narAccessor->readDirectory(dir)) {
+                for (auto & [s2, _type] : narAccessor->readDirectory(dir)) {
                     auto debugPath = dir + "/" + s2;
 
                     if (auto st = narAccessor->stat(debugPath); !st || st->type != SourceAccessor::tRegular
diff --git a/src/libstore/fs-accessor.hh b/src/libstore/fs-accessor.hh
index 1e951ec57..f04a92206 100644
--- a/src/libstore/fs-accessor.hh
+++ b/src/libstore/fs-accessor.hh
@@ -39,7 +39,9 @@ public:
 
     virtual std::optional<Stat> stat(const Path & path) = 0;
 
-    virtual StringSet readDirectory(const Path & path) = 0;
+    using DirEntries = SourceAccessor::DirEntries;
+
+    virtual DirEntries readDirectory(const Path & path) = 0;
 
     /**
      * Read a file inside the store.
diff --git a/src/libstore/local-fs-store.cc b/src/libstore/local-fs-store.cc
index bb83a9cd4..65cbb9e35 100644
--- a/src/libstore/local-fs-store.cc
+++ b/src/libstore/local-fs-store.cc
@@ -48,15 +48,15 @@ struct LocalStoreAccessor : public FSAccessor
             S_ISREG(st.st_mode) && st.st_mode & S_IXUSR}};
     }
 
-    StringSet readDirectory(const Path & path) override
+    DirEntries readDirectory(const Path & path) override
     {
         auto realPath = toRealPath(path);
 
         auto entries = nix::readDirectory(realPath);
 
-        StringSet res;
+        DirEntries res;
         for (auto & entry : entries)
-            res.insert(entry.name);
+            res.insert_or_assign(entry.name, std::nullopt);
 
         return res;
     }
diff --git a/src/libstore/nar-accessor.cc b/src/libstore/nar-accessor.cc
index 43a78a362..fe857a60e 100644
--- a/src/libstore/nar-accessor.cc
+++ b/src/libstore/nar-accessor.cc
@@ -190,16 +190,16 @@ struct NarAccessor : public FSAccessor
         return i->stat;
     }
 
-    StringSet readDirectory(const Path & path) override
+    DirEntries readDirectory(const Path & path) override
     {
         auto i = get(path);
 
         if (i.stat.type != Type::tDirectory)
             throw Error("path '%1%' inside NAR file is not a directory", path);
 
-        StringSet res;
+        DirEntries res;
         for (auto & child : i.children)
-            res.insert(child.first);
+            res.insert_or_assign(child.first, std::nullopt);
 
         return res;
     }
@@ -264,7 +264,7 @@ json listNar(ref<FSAccessor> accessor, const Path & path, bool recurse)
         {
             obj["entries"] = json::object();
             json &res2 = obj["entries"];
-            for (auto & name : accessor->readDirectory(path)) {
+            for (auto & [name, type] : accessor->readDirectory(path)) {
                 if (recurse) {
                     res2[name] = listNar(accessor, path + "/" + name, true);
                 } else
diff --git a/src/libstore/remote-fs-accessor.cc b/src/libstore/remote-fs-accessor.cc
index 6c87ebeaa..21419700c 100644
--- a/src/libstore/remote-fs-accessor.cc
+++ b/src/libstore/remote-fs-accessor.cc
@@ -107,7 +107,7 @@ std::optional<FSAccessor::Stat> RemoteFSAccessor::stat(const Path & path)
     return res.first->stat(res.second);
 }
 
-StringSet RemoteFSAccessor::readDirectory(const Path & path)
+SourceAccessor::DirEntries RemoteFSAccessor::readDirectory(const Path & path)
 {
     auto res = fetch(path);
     return res.first->readDirectory(res.second);
diff --git a/src/libstore/remote-fs-accessor.hh b/src/libstore/remote-fs-accessor.hh
index 5cf759aa0..8de3b7bcd 100644
--- a/src/libstore/remote-fs-accessor.hh
+++ b/src/libstore/remote-fs-accessor.hh
@@ -30,7 +30,7 @@ public:
 
     std::optional<Stat> stat(const Path & path) override;
 
-    StringSet readDirectory(const Path & path) override;
+    DirEntries readDirectory(const Path & path) override;
 
     std::string readFile(const Path & path, bool requireValidPath = true) override;
 
diff --git a/src/nix/ls.cc b/src/nix/ls.cc
index 8dc8a47b4..0ca08cea8 100644
--- a/src/nix/ls.cc
+++ b/src/nix/ls.cc
@@ -74,7 +74,7 @@ struct MixLs : virtual Args, MixJSON
         {
             if (st.type == FSAccessor::Type::tDirectory && !showDirectory) {
                 auto names = accessor->readDirectory(curPath);
-                for (auto & name : names)
+                for (auto & [name, type] : names)
                     showFile(curPath + "/" + name, relPath + "/" + name);
             } else
                 showFile(curPath, relPath);
diff --git a/src/nix/why-depends.cc b/src/nix/why-depends.cc
index 912ba72fb..04c1a0c1c 100644
--- a/src/nix/why-depends.cc
+++ b/src/nix/why-depends.cc
@@ -224,7 +224,7 @@ struct CmdWhyDepends : SourceExprCommand, MixOperateOnOptions
 
                 if (st->type == FSAccessor::Type::tDirectory) {
                     auto names = accessor->readDirectory(p);
-                    for (auto & name : names)
+                    for (auto & [name, type] : names)
                         visitPath(p + "/" + name);
                 }