diff --git a/autotests/batchrenamejobtest.cpp b/autotests/batchrenamejobtest.cpp
--- a/autotests/batchrenamejobtest.cpp
+++ b/autotests/batchrenamejobtest.cpp
@@ -118,7 +118,33 @@
                                                                                     << "##file#5.h"
                                                                                     << "##file#6.c");
 
-    }
+        QTest::newRow("no-extension")                             << (QStringList() << "foo"
+                                                                                    << "bar")
+                                                                  << "FILE#" << 1   << QChar('#')
+                                                                  << (QStringList() << "FILE1"
+                                                                                    << "FILE2");
+
+        QTest::newRow("uppercase-and-lowercase-extensions")                         << (QStringList() << "foo.TXT"
+                                                                                    << "bar.txt")
+                                                                  << "bar#" << 1    << QChar('#')
+                                                                  << (QStringList() << "bar1.TXT"
+                                                                                    << "bar2.txt");
+
+
+        QTest::newRow("mixed-case-extension")                     << (QStringList() << "file20.tXt"
+                                                                                    << "file21.TxT"
+                                                                                    << "file22.TXt")
+                                                                  << "foo#" << 1    << QChar('#')
+                                                                  << (QStringList() << "foo1.tXt"
+                                                                                    << "foo2.TxT"
+                                                                                    << "foo3.TXt");
+
+        QTest::newRow("tar.gz-extension")                         << (QStringList() << "file23.tar.gz"
+                                                                                    << "file24.tar.gz")
+                                                                  << "tar#" << 1    << QChar('#')
+                                                                  << (QStringList() << "tar1.tar.gz"
+                                                                                    << "tar2.tar.gz");
+ }
 
     void batchRenameJobTest()
     {
diff --git a/src/core/batchrenamejob.cpp b/src/core/batchrenamejob.cpp
--- a/src/core/batchrenamejob.cpp
+++ b/src/core/batchrenamejob.cpp
@@ -59,9 +59,8 @@
 
         // Check for extensions.
         QSet<QString> extensions;
-        QMimeDatabase db;
         foreach (const QUrl &url, m_srcList) {
-            const QString extension = db.suffixForFileName(url.toDisplayString().toLower());
+	    const QString extension = fileExtension(url.fileName());
             if (extensions.contains(extension)) {
                 m_allExtensionsDifferent = false;
                 break;
@@ -102,6 +101,7 @@
     Q_DECLARE_PUBLIC(BatchRenameJob)
 
     void slotStart();
+    static QString fileExtension(const QString& filename);
 
     QString indexedName(const QString& name, int index, QChar placeHolder) const;
 
@@ -157,6 +157,26 @@
     return newName;
 }
 
+// The function QMimeDatabase.suffixForFileName always converts the extension to lower case
+// This function is a helper which avoids the conversion to lower case
+QString BatchRenameJobPrivate::fileExtension(const QString& filename)
+{
+    QMimeDatabase db;
+    const size_t extensionLen = db.suffixForFileName(filename).length();
+     
+    //extensionLen will be 0 if the extension is not in the QMimeDatabase i.e "foo.xyz"
+    if (extensionLen) {
+        return filename.right(extensionLen);
+    } else {
+        //Fallback to everything right of the last '.'
+        const int dotIndex = filename.lastIndexOf(QStringLiteral("."));
+        if (dotIndex != -1) {
+            return filename.mid(dotIndex+1);
+        }
+    }
+    return QString();
+}
+
 void BatchRenameJobPrivate::slotStart()
 {
     Q_Q(BatchRenameJob);
@@ -168,8 +188,7 @@
     if (m_listIterator != m_srcList.constEnd()) {
         QString newName = indexedName(m_newName, m_index, m_placeHolder);
         const QUrl oldUrl = *m_listIterator;
-        QMimeDatabase db;
-        const QString extension = db.suffixForFileName(oldUrl.path().toLower());
+        const QString extension = fileExtension(oldUrl.fileName());
         if (!extension.isEmpty()) {
             newName += QLatin1Char('.') + extension;
         }