diff --git a/src/libstore/filetransfer.cc b/src/libstore/filetransfer.cc
index 5ea8b6f962cd..5d4e914a85ba 100644
--- a/src/libstore/filetransfer.cc
+++ b/src/libstore/filetransfer.cc
@@ -54,6 +54,7 @@ struct curlFileTransfer : public FileTransfer
         bool done = false; // whether either the success or failure function has been called
         Callback<FileTransferResult> callback;
         CURL * req = 0;
+        char errbuf[CURL_ERROR_SIZE];
         bool active = false; // whether the handle has been added to the multi object
         std::string statusMsg;
 
@@ -370,6 +371,9 @@ struct curlFileTransfer : public FileTransfer
             if (writtenToSink)
                 curl_easy_setopt(req, CURLOPT_RESUME_FROM_LARGE, writtenToSink);
 
+            curl_easy_setopt(req, CURLOPT_ERRORBUFFER, errbuf);
+            errbuf[0] = 0;
+
             result.data.clear();
             result.bodySize = 0;
         }
@@ -484,8 +488,8 @@ struct curlFileTransfer : public FileTransfer
                         code == CURLE_OK ? "" : fmt(" (curl error: %s)", curl_easy_strerror(code)))
                     : FileTransferError(err,
                         std::move(response),
-                        "unable to %s '%s': %s (%d)",
-                        request.verb(), request.uri, curl_easy_strerror(code), code);
+                        "unable to %s '%s': %s (%d) %s",
+                        request.verb(), request.uri, curl_easy_strerror(code), code, errbuf);
 
                 /* If this is a transient error, then maybe retry the
                    download after a while. If we're writing to a