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());
     }