diff --git a/kdecore/services/kmimetype.cpp b/kdecore/services/kmimetype.cpp
index 21cb7c73..5924edf2 100644
--- a/kdecore/services/kmimetype.cpp
+++ b/kdecore/services/kmimetype.cpp
@@ -200,9 +200,8 @@ KMimeType::Ptr KMimeType::findByUrlHelper( const KUrl& _url, mode_t mode,
 
     // Try the magic matches (if we can read the data)
     if ( device ) {
-        QByteArray cache;
         int magicAccuracy;
-        KMimeType::Ptr mime = KMimeTypeRepository::self()->findFromContent(device, &magicAccuracy, cache);
+        KMimeType::Ptr mime = KMimeTypeRepository::self()->findFromContent(device, &magicAccuracy);
         // mime can't be 0, except in case of install problems.
         // However we get magicAccuracy==0 for octet-stream, i.e. no magic match found.
         //kDebug(servicesDebugArea()) << "findFromContent said" << (mime?mime->name():QString()) << "with accuracy" << magicAccuracy;
@@ -328,14 +327,12 @@ KMimeType::Ptr KMimeType::findByContent( const QByteArray &data, int *accuracy )
 {
     QBuffer buffer(const_cast<QByteArray *>(&data));
     buffer.open(QIODevice::ReadOnly);
-    QByteArray cache;
-    return KMimeTypeRepository::self()->findFromContent(&buffer, accuracy, cache);
+    return KMimeTypeRepository::self()->findFromContent(&buffer, accuracy);
 }
 
 KMimeType::Ptr KMimeType::findByContent( QIODevice* device, int* accuracy )
 {
-    QByteArray cache;
-    return KMimeTypeRepository::self()->findFromContent(device, accuracy, cache);
+    return KMimeTypeRepository::self()->findFromContent(device, accuracy);
 }
 
 KMimeType::Ptr KMimeType::findByFileContent( const QString &fileName, int *accuracy )
@@ -356,8 +353,7 @@ KMimeType::Ptr KMimeType::findByFileContent( const QString &fileName, int *accur
         return KMimeType::defaultMimeTypePtr();
     }
 
-    QByteArray cache;
-    return KMimeTypeRepository::self()->findFromContent(&device, accuracy, cache);
+    return KMimeTypeRepository::self()->findFromContent(&device, accuracy);
 }
 
 bool KMimeType::isBinaryData( const QString &fileName )
diff --git a/kdecore/services/kmimetyperepository.cpp b/kdecore/services/kmimetyperepository.cpp
index 9adde950..419fcaa0 100644
--- a/kdecore/services/kmimetyperepository.cpp
+++ b/kdecore/services/kmimetyperepository.cpp
@@ -228,7 +228,7 @@ QStringList KMimeTypeRepository::findFromFileName(const QString &fileName, QStri
     return matchingMimeTypes;
 }
 
-KMimeType::Ptr KMimeTypeRepository::findFromContent(QIODevice* device, int* accuracy, QByteArray& beginning)
+KMimeType::Ptr KMimeTypeRepository::findFromContent(QIODevice* device, int* accuracy)
 {
     Q_ASSERT(device->isOpen());
     const qint64 deviceSize = device->size();
@@ -237,13 +237,11 @@ KMimeType::Ptr KMimeTypeRepository::findFromContent(QIODevice* device, int* accu
             *accuracy = 100;
         return findMimeTypeByName(QLatin1String("application/x-zerosize"));
     }
-    if (beginning.isEmpty()) {
-        // check if we can really read the data; also provide enough data for most rules
-        const qint64 dataNeeded = qMin(deviceSize, (qint64) 16384);
-        beginning.resize(dataNeeded);
-        if (!device->seek(0) || device->read(beginning.data(), dataNeeded) == -1) {
-            return defaultMimeTypePtr(); // don't bother detecting unreadable file
-        }
+    // check if we can really read the data; also provide enough data for most rules
+    const qint64 dataNeeded = qMin(deviceSize, (qint64) 16384);
+    QByteArray beginning(dataNeeded, '\0');
+    if (!device->seek(0) || device->read(beginning.data(), dataNeeded) == -1) {
+        return defaultMimeTypePtr(); // don't bother detecting unreadable file
     }
 
     parseMagic();
diff --git a/kdecore/services/kmimetyperepository_p.h b/kdecore/services/kmimetyperepository_p.h
index 3d4c6b76..263d7ec7 100644
--- a/kdecore/services/kmimetyperepository_p.h
+++ b/kdecore/services/kmimetyperepository_p.h
@@ -104,11 +104,10 @@ private: // only for KMimeType and unittests
      * Find a mimetype from the content of a file or buffer
      * @param device the file or buffer. Must be open.
      * @param accuracy returns the priority of the rule that matched
-     * @param beginning will contain the first N bytes of the device; used as cache to avoid repeated seeks
      *
      * This is internal API, use KMimeType::findByUrl instead.
      */
-    KMimeType::Ptr findFromContent(QIODevice* device, int* accuracy, QByteArray& beginning);
+    KMimeType::Ptr findFromContent(QIODevice* device, int* accuracy);
 
     /**
      * @return true if at least one mimetype is present