diff -up qtbase-opensource-src-5.9.4/src/corelib/mimetypes/qmimetype.cpp.fdo101667 qtbase-opensource-src-5.9.4/src/corelib/mimetypes/qmimetype.cpp

--- qtbase-opensource-src-5.9.4/src/corelib/mimetypes/qmimetype.cpp.fdo101667	2018-01-16 00:53:43.000000000 -0600

+++ qtbase-opensource-src-5.9.4/src/corelib/mimetypes/qmimetype.cpp	2018-01-28 07:18:09.502534397 -0600

@@ -418,6 +418,8 @@ QStringList QMimeType::suffixes() const

  */

 QString QMimeType::preferredSuffix() const

 {

+    if (isDefault()) // workaround for unwanted *.bin suffix for octet-stream, https://bugs.freedesktop.org/show_bug.cgi?id=101667, fixed upstream in 1.10 

+        return QString();

     const QStringList suffixList = suffixes();

     return suffixList.isEmpty() ? QString() : suffixList.at(0);

 }