diff --git a/src/libstore/binary-cache-store.cc b/src/libstore/binary-cache-store.cc
index 804e3f6aa..d8e68fd58 100644
--- a/src/libstore/binary-cache-store.cc
+++ b/src/libstore/binary-cache-store.cc
@@ -97,7 +97,7 @@ void BinaryCacheStore::init()
 
     auto cacheInfo = getFile(cacheInfoFile);
     if (!cacheInfo) {
-        upsertFile(cacheInfoFile, "StoreDir: " + storeDir + "\n");
+        upsertFile(cacheInfoFile, "StoreDir: " + storeDir + "\n", "text/x-nix-cache-info");
     } else {
         for (auto & line : tokenizeString<Strings>(*cacheInfo, "\n")) {
             size_t colon = line.find(':');
@@ -224,7 +224,7 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
             }
         }
 
-        upsertFile(storePathToHash(info.path) + ".ls.xz", *compress("xz", jsonOut.str()));
+        upsertFile(storePathToHash(info.path) + ".ls.xz", *compress("xz", jsonOut.str()), "application/x-nix-nar-listing");
     }
 
     else {
@@ -254,7 +254,7 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
            "");
     if (repair || !fileExists(narInfo->url)) {
         stats.narWrite++;
-        upsertFile(narInfo->url, *narCompressed);
+        upsertFile(narInfo->url, *narCompressed, "application/x-nix-nar");
     } else
         stats.narWriteAverted++;
 
@@ -265,7 +265,7 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
     /* Atomically write the NAR info file.*/
     if (secretKey) narInfo->sign(*secretKey);
 
-    upsertFile(narInfoFile, narInfo->to_string());
+    upsertFile(narInfoFile, narInfo->to_string(), "text/x-nix-narinfo");
 
     auto hashPart = storePathToHash(narInfo->path);
 
diff --git a/src/libstore/binary-cache-store.hh b/src/libstore/binary-cache-store.hh
index 1c287056c..d42b1abd2 100644
--- a/src/libstore/binary-cache-store.hh
+++ b/src/libstore/binary-cache-store.hh
@@ -31,7 +31,9 @@ public:
 
     virtual bool fileExists(const std::string & path) = 0;
 
-    virtual void upsertFile(const std::string & path, const std::string & data) = 0;
+    virtual void upsertFile(const std::string & path,
+        const std::string & data,
+        const std::string & mimeType) = 0;
 
     /* Return the contents of the specified file, or null if it
        doesn't exist. */
diff --git a/src/libstore/http-binary-cache-store.cc b/src/libstore/http-binary-cache-store.cc
index 9d31f77c9..37a7d6ace 100644
--- a/src/libstore/http-binary-cache-store.cc
+++ b/src/libstore/http-binary-cache-store.cc
@@ -64,7 +64,9 @@ protected:
         }
     }
 
-    void upsertFile(const std::string & path, const std::string & data) override
+    void upsertFile(const std::string & path,
+        const std::string & data,
+        const std::string & mimeType) override
     {
         throw UploadToHTTP("uploading to an HTTP binary cache is not supported");
     }
diff --git a/src/libstore/local-binary-cache-store.cc b/src/libstore/local-binary-cache-store.cc
index 0f377989b..aff22f9fc 100644
--- a/src/libstore/local-binary-cache-store.cc
+++ b/src/libstore/local-binary-cache-store.cc
@@ -30,7 +30,9 @@ protected:
 
     bool fileExists(const std::string & path) override;
 
-    void upsertFile(const std::string & path, const std::string & data) override;
+    void upsertFile(const std::string & path,
+        const std::string & data,
+        const std::string & mimeType) override;
 
     void getFile(const std::string & path,
         std::function<void(std::shared_ptr<std::string>)> success,
@@ -83,7 +85,9 @@ bool LocalBinaryCacheStore::fileExists(const std::string & path)
     return pathExists(binaryCacheDir + "/" + path);
 }
 
-void LocalBinaryCacheStore::upsertFile(const std::string & path, const std::string & data)
+void LocalBinaryCacheStore::upsertFile(const std::string & path,
+    const std::string & data,
+    const std::string & mimeType)
 {
     atomicWrite(binaryCacheDir + "/" + path, data);
 }
diff --git a/src/libstore/s3-binary-cache-store.cc b/src/libstore/s3-binary-cache-store.cc
index 1d44e6832..5ecf3996d 100644
--- a/src/libstore/s3-binary-cache-store.cc
+++ b/src/libstore/s3-binary-cache-store.cc
@@ -148,7 +148,7 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
         : S3BinaryCacheStore(params)
         , bucketName(bucketName)
         , s3Helper(get(params, "aws-region", Aws::Region::US_EAST_1))
-        , textCompression(get(params, "text-compression", "gzip"))
+        , textCompression(get(params, "text-compression", ""))
         , logCompression(get(params, "log-compression", textCompression))
     {
         diskCache = getNarInfoDiskCache();
@@ -229,6 +229,7 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
     }
 
     void uploadFile(const std::string & path, const std::string & data,
+        const std::string & mimeType,
         const std::string & contentEncoding)
     {
         auto request =
@@ -236,6 +237,8 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
             .WithBucket(bucketName)
             .WithKey(path);
 
+        request.SetContentType(mimeType);
+
         if (contentEncoding != "")
             request.SetContentEncoding(contentEncoding);
 
@@ -261,14 +264,15 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
         stats.putTimeMs += duration;
     }
 
-    void upsertFile(const std::string & path, const std::string & data) override
+    void upsertFile(const std::string & path, const std::string & data,
+        const std::string & mimeType) override
     {
         if (path.find(".narinfo") != std::string::npos)
-            uploadFile(path, *compress(textCompression, data), textCompression);
+            uploadFile(path, *compress(textCompression, data), mimeType, textCompression);
         else if (path.find("/log") != std::string::npos)
-            uploadFile(path, *compress(logCompression, data), logCompression);
+            uploadFile(path, *compress(logCompression, data), mimeType, logCompression);
         else
-            uploadFile(path, data, "");
+            uploadFile(path, data, mimeType, "");
     }
 
     void getFile(const std::string & path,