Millicode store access checking instructions are provided via an operand access control register (OACR) including a test modifier indicator, which is communicatively coupled to an instruction unit subsystem, the instruction unit subsystem for fetching and decoding instructions. The instructions include a millicode instruction with an operand defining an address to check for a store access exception. In addition, an execution unit for executing the millicode instruction performs a method. The method includes receiving the millicode instruction from the instruction unit subsystem, testing for the store access exception at the address as if the test modifier is set absent an update to the OACR, and outputting a result of the testing for the store access exception.