diff --git a/src/plugins/platforms/windows/qwindowsfontdatabase.cpp b/src/plugins/platforms/windows/qwindowsfontdatabase.cpp
index d1c0249116..b979dc6c4e 100644
--- a/src/plugins/platforms/windows/qwindowsfontdatabase.cpp
+++ b/src/plugins/platforms/windows/qwindowsfontdatabase.cpp
@@ -303,8 +303,7 @@ namespace {
             , m_referenceCount(0)
         {
         }
-
-        ~DirectWriteFontFileStream()
+        virtual ~DirectWriteFontFileStream()
         {
         }
 
@@ -355,7 +354,7 @@ namespace {
         OUT void **fragmentContext)
     {
         *fragmentContext = NULL;
-        if (fragmentSize + fileOffset <= m_fontData.size()) {
+        if (fileOffset + fragmentSize <= quint64(m_fontData.size())) {
             *fragmentStart = m_fontData.data() + fileOffset;
             return S_OK;
         } else {
@@ -384,8 +383,7 @@ namespace {
     {
     public:
         DirectWriteFontFileLoader() : m_referenceCount(0) {}
-
-        ~DirectWriteFontFileLoader()
+        virtual ~DirectWriteFontFileLoader()
         {
         }
 
diff --git a/src/plugins/platforms/windows/qwindowsfontenginedirectwrite.cpp b/src/plugins/platforms/windows/qwindowsfontenginedirectwrite.cpp
index 85cd92b234..75449e22ed 100644
--- a/src/plugins/platforms/windows/qwindowsfontenginedirectwrite.cpp
+++ b/src/plugins/platforms/windows/qwindowsfontenginedirectwrite.cpp
@@ -33,6 +33,10 @@
 
 #ifndef QT_NO_DIRECTWRITE
 
+#if WINVER < 0x0600
+#  undef WINVER
+#  define WINVER 0x0600
+#endif
 #if _WIN32_WINNT < 0x0600
 #undef _WIN32_WINNT
 #define _WIN32_WINNT 0x0600
@@ -61,10 +65,14 @@ namespace {
     class GeometrySink: public IDWriteGeometrySink
     {
     public:
-        GeometrySink(QPainterPath *path) : m_path(path), m_refCount(0)
+        GeometrySink(QPainterPath *path)
+            : m_refCount(0), m_path(path)
         {
             Q_ASSERT(m_path != 0);
         }
+        virtual ~GeometrySink()
+        {
+        }
 
         IFACEMETHOD_(void, AddBeziers)(const D2D1_BEZIER_SEGMENT *beziers, UINT bezierCount);
         IFACEMETHOD_(void, AddLines)(const D2D1_POINT_2F *points, UINT pointCount);