Format preserving encryption of object code is disclosed. One example is a system including at least one processor and a memory storing instructions executable by the at least one processor to identify object code to be secured, where the object code comprises a list of instructions, each instruction comprising an opcode and zero or more parameters. A format preserving encryption (FPE) is applied to the received object code, where the FPE is applied separately to a sub-plurality of instructions in the list of instructions, to generate an encrypted object code comprising a sub-plurality of encrypted instructions. An encrypted object code is provided to a service provider, where the encrypted object code comprises the sub-plurality of encrypted instructions, and any unencrypted portions of the object code.