A method of checking the integrity of a dynamic link library (DLL) file called by an application being executed on a handheld medical device is described. The method includes loading a DLL from a read only memory (ROM) to a random access memory (RAM) beginning at a fixed location in the RAM. The DLL includes a first routine for performing a safety critical function of the handheld medical device and a second routine for performing a cyclical redundancy check (CRC) once the DLL is loaded to the RAM. The method includes selectively executing the first routine from the RAM. The method includes selectively executing the second routine from the RAM including: calculating a check value based on the DLL; comparing the check value with a predetermined check value; and indicating that an error is present when the check value is different than the predetermined check value.