A method and system for nearly immediately trapping a failure-to-check-a-return-value error in a computer program. Modern processor architectures, such as the Intel IA-64 processor architecture, provide for control speculation of load instructions, including 1-bit NAT registers, associated with general registers, that indicate occurrences of deferred exceptions arising during execution of control-speculative load instructions targeting the corresponding general registers. One embodiment of the present invention employs the NAT registers associated with general-purpose registers to distinguish special values, often indicating error conditions, stored in general-purpose registers serving to store the return values of functions and routines.