diff --git a/src/filewidgets/kfilewidget.cpp b/src/filewidgets/kfilewidget.cpp
--- a/src/filewidgets/kfilewidget.cpp
+++ b/src/filewidgets/kfilewidget.cpp
@@ -2258,7 +2258,8 @@
                 }
             }
 
-            if (!currentExtension.isEmpty() && extensionList.contains(QLatin1String("*.") + currentExtension)) {
+            if ((!currentExtension.isEmpty() && extensionList.contains(QLatin1String("*.") + currentExtension))
+                    || filter == QStringLiteral("application/octet-stream")) {
                 extension = QLatin1Char('.') + currentExtension;
             } else {
                 extension = defaultExtension;