qwaylandshmbackingstore.cpp:290:5: error: ‘qssize_t’ was not declared in this scope

qwaylandshmbackingstore.cpp: In member function ‘void QtWaylandClient::QWaylandShmBackingStore::resize(const QSize&)’:
qwaylandshmbackingstore.cpp:290:5: error: ‘qssize_t’ was not declared in this scope
     qssize_t oldSize = mBackBuffer ? mBackBuffer->image()->sizeInBytes() : 0;
     ^~~~~~~~
qwaylandshmbackingstore.cpp:292:34: error: ‘oldSize’ was not declared in this scope
     if (mBackBuffer != buffer && oldSize == buffer->image()->sizeInBytes()) {
                                  ^~~~~~~
Makefile:3180: recipe for target '.obj/qwaylandshmbackingstore.o' failed
make[2]: *** [.obj/qwaylandshmbackingstore.o] Error 1
make[2]: *** Waiting for unfinished jobs....