diff --git a/src/corelib/text/qbytearray.cpp b/src/corelib/text/qbytearray.cpp
index 826c0b2be0..f5b468ad6e 100644
--- a/src/corelib/text/qbytearray.cpp
+++ b/src/corelib/text/qbytearray.cpp
@@ -633,7 +633,8 @@ QByteArray qUncompress(const uchar* data, qsizetype nbytes)
     if (len > MaxDecompressedSize)
         return invalidCompressedData();
 
-    QByteArray::DataPointer d(QByteArray::Data::allocate(len));
+    Q_ASSERT(len <= size_t((std::numeric_limits<qsizetype>::max)()));
+    QByteArray::DataPointer d(QByteArray::Data::allocate(qsizetype(len)));
     if (d.data() == nullptr) // allocation failed
         return invalidCompressedData();