The advantage of random testing is that test application can be performed at a low cost in the BIST scheme. However, not all circuits are random pattern testable. In this paper, we present a method for improving random pattern testability of logic circuits by partial circuit duplication. The basic idea i s to detect random pattern resistant faults by using the difference between the duplicated part of a circuit and the original part. Experimental results on benchmark circuits show that high fault coverage can be achieved with a very small amount of hardware overhead.