diff --git a/engines/wintermute/base/gfx/osystem/base_render_osystem.cpp b/engines/wintermute/base/gfx/osystem/base_render_osystem.cpp
index 0e7e5aa8197d..668105457fd1 100644
--- a/engines/wintermute/base/gfx/osystem/base_render_osystem.cpp
+++ b/engines/wintermute/base/gfx/osystem/base_render_osystem.cpp
@@ -613,8 +613,8 @@ bool BaseRenderOSystem::setViewport(int left, int top, int right, int bottom) {
 	// TODO: Hopefully this is the same logic that ScummVM uses.
 	rect.left = (int16)(left + _borderLeft);
 	rect.top = (int16)(top + _borderTop);
-	rect.right = (int16)((right - left) * _ratioX);
-	rect.bottom = (int16)((bottom - top) * _ratioY);
+	rect.setWidth((int16)((right - left) * _ratioX));
+	rect.setHeight((int16)((bottom - top) * _ratioY));
 
 	_renderRect = rect;
 	return STATUS_OK;