diff --git a/src/video/opengl.cpp b/src/video/opengl.cpp
index 362636a832..6cfeafad3f 100644
--- a/src/video/opengl.cpp
+++ b/src/video/opengl.cpp
@@ -1157,7 +1157,7 @@ void *OpenGLBackend::GetVideoBuffer()
 		this->vid_buffer = _glMapBuffer(GL_PIXEL_UNPACK_BUFFER, GL_READ_WRITE);
 	} else if (this->vid_buffer == nullptr) {
 		_glBindBuffer(GL_PIXEL_UNPACK_BUFFER, this->vid_pbo);
-		this->vid_buffer = _glMapBufferRange(GL_PIXEL_UNPACK_BUFFER, 0, _screen.pitch * _screen.height * BlitterFactory::GetCurrentBlitter()->GetScreenDepth() / 8, GL_MAP_READ_BIT | GL_MAP_WRITE_BIT | GL_MAP_PERSISTENT_BIT | GL_MAP_COHERENT_BIT);
+		this->vid_buffer = _glMapBufferRange(GL_PIXEL_UNPACK_BUFFER, 0, static_cast<GLsizeiptr>(_screen.pitch) * _screen.height * BlitterFactory::GetCurrentBlitter()->GetScreenDepth() / 8, GL_MAP_READ_BIT | GL_MAP_WRITE_BIT | GL_MAP_PERSISTENT_BIT | GL_MAP_COHERENT_BIT);
 	}
 
 	return this->vid_buffer;