Two years after he was granted the patent Dunlop was officially informed that it was invalid as Scottish inventor Robert William Thomson (1822–1873) had patented the idea in France in 1846 and in the US in 1847.
Men to år efter han fik patentet, fik han officielt at vide at det var ugyldigt, da den skotske opfinder Robert William Thomson (1822 – 1873), havde patenteret ideen i Frankrig i 1846 og i USA i 1847.