diff --git a/CHANGELOG.md b/CHANGELOG.md
index 93137569..fff45755 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+v0.6.91
+* Bug fix
+
 v0.6.90
 * [cli] Support for writing files up to 4gb on most computers (2gb was the previous limit).
 
diff --git a/package-lock.json b/package-lock.json
index 5745731d..c764ef29 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "mapshaper",
-  "version": "0.6.90",
+  "version": "0.6.91",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "mapshaper",
-      "version": "0.6.90",
+      "version": "0.6.91",
       "license": "MPL-2.0",
       "dependencies": {
         "@placemarkio/tokml": "^0.3.3",
diff --git a/package.json b/package.json
index 56fe968d..3774c381 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "mapshaper",
-  "version": "0.6.90",
+  "version": "0.6.91",
   "description": "A tool for editing vector datasets for mapping and GIS.",
   "keywords": [
     "shapefile",
diff --git a/src/gui/gui-proxy.mjs b/src/gui/gui-proxy.mjs
index 79c11720..9992db46 100644
--- a/src/gui/gui-proxy.mjs
+++ b/src/gui/gui-proxy.mjs
@@ -50,7 +50,7 @@ export function WriteFilesProxy(gui) {
         await internal.writeFiles(files, {save_to_download_folder: true});
       }
     } else if (files.length == 1) {
-      await gui.promisify(saveBlobToLocalFile)(files[0].filename, new Blob([files[0].content]));
+      await utils.promisify(saveBlobToLocalFile)(files[0].filename, new Blob([files[0].content]));
     } else {
       filename = internal.getCommonFileBase(utils.pluck(files, 'filename')) || "output";
       await utils.promisify(saveZipFile)(filename + ".zip", files);