Abstract: Apparatus and associated methods relate to compacting scan chain output responses of vectors into an on-chip multiple-input shift register (MISR) in the presence of unknown/indeterministic values X in design. In an illustrative example, a system may include a processing engine configured to generate a control signal for a MISR, and the control signal may hold information of what cycle has deterministic output response. The MISR may be configured to compact deterministic output responses of actual scan chain output responses in response to the decoded control signal and compare on-chip MISR signatures with expected MISR signatures to generate pass/fail status of the test. By using the system, unknown/indeterministic values X on the output responses may be blocked from being compacted into the MISR. Accordingly, the on-chip MISR signatures may not be corrupted by the unknown/indeterministic values X, and accuracy of the scan test may be advantageously improved.