diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index 514ab3bf9..25dab18bb 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -696,6 +696,8 @@ struct curlFileTransfer : public FileTransfer
                 std::string scheme = get(params, "scheme").value_or("");
                 std::string endpoint = get(params, "endpoint").value_or("");
 
+                debug("enqueueFileTransfer: scheme: %s", scheme);
+
                 S3Helper s3Helper(profile, region, scheme, endpoint);
 
                 // FIXME: implement ETag
diff --git a/src/libstore/s3-binary-cache-store.cc b/src/libstore/s3-binary-cache-store.cc
index 6bfbee044..ff406e5e4 100644
--- a/src/libstore/s3-binary-cache-store.cc
+++ b/src/libstore/s3-binary-cache-store.cc
@@ -126,6 +126,7 @@ ref<Aws::Client::ClientConfiguration> S3Helper::makeConfig(const string & region
     initAWS();
     auto res = make_ref<Aws::Client::ClientConfiguration>();
     res->region = region;
+    debug("configuring scheme %s", scheme);
     if (!scheme.empty()) {
         res->scheme = Aws::Http::SchemeMapper::FromString(scheme.c_str());
     }