diff --git a/ghost/admin/app/components/modals/upload-theme.js b/ghost/admin/app/components/modals/upload-theme.js
index 184d7e6607..dd600589ff 100644
--- a/ghost/admin/app/components/modals/upload-theme.js
+++ b/ghost/admin/app/components/modals/upload-theme.js
@@ -47,7 +47,8 @@ export default ModalComponent.extend({
 
     actions: {
         validateTheme(file) {
-            let themeName = file.name.replace(/\.zip$/, '');
+            let themeName = file.name.replace(/\.zip$/, '').replace(/[^\w@.]/gi, '-');
+
             let availableThemeNames = this.get('availableThemeNames');
 
             this.set('file', file);