Unintended failures during a computation are painful but frequent during software development. Failures due to external reasons (e.g., missing files, no permissions) can be caught by exception handlers. Programming failures, such as calling a partially defined operation with unintended arguments, are often not caught due to the assumption that the software is correct. This paper presents an approach to verify such assumptions. For this purpose, non-failure conditions for operations are inferred and then checked in all uses of partially defined operations. In the positive case, the absence of such failures is ensured. In the negative case, the programmer could adapt the program to handle possibly failing situations and check the program again. Our method is fully automatic and can be applied to larger declarative programs. The results of an implementation for functional logic Curry programs are presented.