This paper investigates empirically whether the ASEAN Free Trade Agreement had a building bloc or stumbling bloc effect on subsequent changes in MFN tariffs of four major ASEAN members. The method resembles the one recently used by Nuno Limão. We use tariff data to test whether MFN tariffs were changed differently for preferential products compared to otherwise similar products without a preference. We find a significant building bloc effect for Indonesia, the Philippines and Thailand. MFN tariffs of preferential products were reduced by more than for non-preferential products. We obtain ambiguous effects for Malaysia. This suggests that overall the ASEAN Free Trade Agreement has rather helped than hindered nondiscriminatory trade liberalization.