diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 3705f3d4d..9bb81add7 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -76,9 +76,10 @@ std::optional<std::string> BinaryCacheStore::getNixCacheInfo()
     return getFile(cacheInfoFile);
 }
 
-void BinaryCacheStore::upsertFile(const std::string & path, std::string && data, const std::string & mimeType)
+void BinaryCacheStore::upsertFile(
+    const std::string & path, std::string && data, const std::string & mimeType, uint64_t sizeHint)
 {
-    upsertFile(path, std::make_shared<std::stringstream>(std::move(data)), mimeType);
+    upsertFile(path, std::make_shared<std::stringstream>(std::move(data)), mimeType, sizeHint);
 }
 
 void BinaryCacheStore::getFile(const std::string & path, Callback<std::optional<std::string>> callback) noexcept
@@ -274,7 +275,8 @@ ref<const ValidPathInfo> BinaryCacheStore::addToStoreCommon(
         upsertFile(
             narInfo->url,
             std::make_shared<std::fstream>(fnTemp, std::ios_base::in | std::ios_base::binary),
-            "application/x-nix-nar");
+            "application/x-nix-nar",
+            narInfo->fileSize);
     } else
         stats.narWriteAverted++;
 
diff --git a/src/libstore/http-binary-cache-store.cc b/src/libstore/http-binary-cache-store.cc
index 5c455dd04..7883161d5 100644
--- a/src/libstore/http-binary-cache-store.cc
+++ b/src/libstore/http-binary-cache-store.cc
@@ -155,7 +155,8 @@ protected:
     void upsertFile(
         const std::string & path,
         std::shared_ptr<std::basic_iostream<char>> istream,
-        const std::string & mimeType) override
+        const std::string & mimeType,
+        uint64_t sizeHint) override
     {
         auto req = makeRequest(path);
 
diff --git a/src/libstore/include/nix/store/binary-cache-store.hh b/src/libstore/include/nix/store/binary-cache-store.hh
index 3f4de2bd4..0bed09aec 100644
--- a/src/libstore/include/nix/store/binary-cache-store.hh
+++ b/src/libstore/include/nix/store/binary-cache-store.hh
@@ -101,13 +101,27 @@ public:
     virtual bool fileExists(const std::string & path) = 0;
 
     virtual void upsertFile(
-        const std::string & path, std::shared_ptr<std::basic_iostream<char>> istream, const std::string & mimeType) = 0;
+        const std::string & path,
+        std::shared_ptr<std::basic_iostream<char>> istream,
+        const std::string & mimeType,
+        uint64_t sizeHint) = 0;
 
     void upsertFile(
         const std::string & path,
         // FIXME: use std::string_view
         std::string && data,
-        const std::string & mimeType);
+        const std::string & mimeType,
+        uint64_t sizeHint);
+
+    void upsertFile(
+        const std::string & path,
+        // FIXME: use std::string_view
+        std::string && data,
+        const std::string & mimeType)
+    {
+        auto size = data.size();
+        upsertFile(path, std::move(data), mimeType, size);
+    }
 
     /**
      * Dump the contents of the specified file to a sink.
diff --git a/src/libstore/local-binary-cache-store.cc b/src/libstore/local-binary-cache-store.cc
index b5e43de68..c1811bf17 100644
--- a/src/libstore/local-binary-cache-store.cc
+++ b/src/libstore/local-binary-cache-store.cc
@@ -56,7 +56,8 @@ protected:
     void upsertFile(
         const std::string & path,
         std::shared_ptr<std::basic_iostream<char>> istream,
-        const std::string & mimeType) override
+        const std::string & mimeType,
+        uint64_t sizeHint) override
     {
         auto path2 = config->binaryCacheDir + "/" + path;
         static std::atomic<int> counter{0};