diff --git a/src/widgets/accessmanagerreply_p.h b/src/widgets/accessmanagerreply_p.h
--- a/src/widgets/accessmanagerreply_p.h
+++ b/src/widgets/accessmanagerreply_p.h
@@ -96,6 +96,7 @@
 
 private:
     QByteArray m_data;
+    qint64 m_offset;
     bool m_metaDataRead;
     bool m_ignoreContentDisposition;
     bool m_emitReadyReadOnMetaDataChange;
diff --git a/src/widgets/accessmanagerreply_p.cpp b/src/widgets/accessmanagerreply_p.cpp
--- a/src/widgets/accessmanagerreply_p.cpp
+++ b/src/widgets/accessmanagerreply_p.cpp
@@ -46,6 +46,7 @@
                                        bool emitReadyReadOnMetaDataChange,
                                        QObject *parent)
     : QNetworkReply(parent),
+      m_offset(0),
       m_metaDataRead(false),
       m_ignoreContentDisposition(false),
       m_emitReadyReadOnMetaDataChange(emitReadyReadOnMetaDataChange),
@@ -84,6 +85,7 @@
                                        QObject *parent)
     : QNetworkReply(parent),
       m_data(data),
+      m_offset(0),
       m_ignoreContentDisposition(false),
       m_emitReadyReadOnMetaDataChange(false)
 {
@@ -106,7 +108,8 @@
                                        QNetworkReply::NetworkError errorCode,
                                        const QString &errorMessage,
                                        QObject *parent)
-    : QNetworkReply(parent)
+    : QNetworkReply(parent),
+      m_offset(0)
 {
     setRequest(request);
     setOpenMode(QIODevice::ReadOnly);
@@ -131,21 +134,31 @@
     }
     m_kioJob.clear();
     m_data.clear();
+    m_offset = 0;
     m_metaDataRead = false;
 }
 
 qint64 AccessManagerReply::bytesAvailable() const
 {
-    return (QNetworkReply::bytesAvailable() + m_data.length());
+    return (QNetworkReply::bytesAvailable() + m_data.length() - m_offset);
 }
 
 qint64 AccessManagerReply::readData(char *data, qint64 maxSize)
 {
-    const qint64 length = qMin(qint64(m_data.length()), maxSize);
+    const qint64 length = qMin(qint64(m_data.length() - m_offset), maxSize);
+
+    if (length <= 0)
+        return 0;
+
+    memcpy(data, m_data.constData() + m_offset, length);
+    m_offset += length;
 
-    if (length) {
-        memcpy(data, m_data.constData(), length);
-        m_data.remove(0, length);
+    // Remove the stale data before m_offset only if it grows to half
+    // of the total size, to avoid calling the expensive .remove function.
+    // If there's no data left, it's a trivial remove.
+    if (m_data.length() == m_offset || m_offset * 2 >= m_data.length()) {
+        m_data.remove(0, m_offset);
+        m_offset = 0;
     }
 
     return length;