The rupee strengthened marginally by 4 paise to 51 rupees 86 paise per dollar in early trade on the Interbank Foreign Exchange today, supported by continued foreign fund inflows.Dealers said consistent dollar inflows and selling of the American currency by exporters, mainly supported the rupee.The rupee had lost 20 paise to close at Rs 51.90 per dollar on Wednesday on the emergence of dollar demand from importers.