diff --git a/src/gui/painting/qdrawhelper.cpp b/src/gui/painting/qdrawhelper.cpp
index 1c62d54fcdb..117f43db8fd 100644
--- a/src/gui/painting/qdrawhelper.cpp
+++ b/src/gui/painting/qdrawhelper.cpp
@@ -3779,7 +3779,8 @@ static void spanfill_from_first(QRasterBuffer *rasterBuffer, QPixelLayout::BPP b
 #define QT_THREAD_PARALLEL_FILLS(function) \
     const int segments = (count + 32) / 64; \
     QThreadPool *threadPool = QThreadPoolPrivate::qtGuiInstance(); \
-    if (segments > 1 && threadPool && !threadPool->contains(QThread::currentThread())) { \
+    if (segments > 1 && qPixelLayouts[data->rasterBuffer->format].bpp >= QPixelLayout::BPP8 \
+             && threadPool && !threadPool->contains(QThread::currentThread())) { \
         QSemaphore semaphore; \
         int c = 0; \
         for (int i = 0; i < segments; ++i) { \