diff --git a/src/mako/api/lib/mbuild.mako b/src/mako/api/lib/mbuild.mako
index 94abe2106b..b6af9cfd9a 100644
--- a/src/mako/api/lib/mbuild.mako
+++ b/src/mako/api/lib/mbuild.mako
@@ -800,7 +800,7 @@ else {
                         let upload_result = {
                             let url_str = &res.headers.get::<Location>().expect("Location header is part of protocol").0;
                             if upload_url_from_server {
-                                dlg.store_upload_url(url_str);
+                                dlg.store_upload_url(Some(url_str));
                             }
 
                             cmn::ResumableUploadHelper {
@@ -832,6 +832,7 @@ else {
                                 res = upload_result;
                                 if !res.status.is_success() {
                                     ## delegate was called in upload() already - don't tell him again
+                                    dlg.store_upload_url(None);
                                     ${delegate_finish}(false);
                                     return Err(Error::Failure(res))
                                 }
diff --git a/src/rust/api/cmn.rs b/src/rust/api/cmn.rs
index cd013bd649..44e55348f2 100644
--- a/src/rust/api/cmn.rs
+++ b/src/rust/api/cmn.rs
@@ -171,7 +171,10 @@ pub trait Delegate {
     /// Called after we have retrieved a new upload URL for a resumable upload to store it
     /// in case we fail or cancel. That way, we can attempt to resume the upload later, 
     /// see `upload_url()`.
-    fn store_upload_url(&mut self, url: &str) {
+    /// It will also be called with None after a successful upload, which allows the delegate
+    /// to forget the URL. That way, we will not attempt to resume an upload that has already
+    /// finished.
+    fn store_upload_url(&mut self, url: Option<&str>) {
         let _ = url;
     }