diff --git a/sys/opencrypto/crypto.c b/sys/opencrypto/crypto.c
--- a/sys/opencrypto/crypto.c
+++ b/sys/opencrypto/crypto.c
@@ -1372,6 +1372,11 @@
 	if (out == NULL) {
 		KASSERT(crp->crp_payload_output_start == 0,
 		    ("payload output start non-zero without output buffer"));
+	} else if (csp->csp_mode == CSP_MODE_DIGEST) {
+		KASSERT(!(crp->crp_op & CRYPTO_OP_VERIFY_DIGEST),
+		    ("digest verify with separate output buffer"));
+		KASSERT(crp->crp_payload_output_start == 0,
+		    ("digest operation with non-zero payload output start"));
 	} else {
 		KASSERT(crp->crp_payload_output_start == 0 ||
 		    crp->crp_payload_output_start < olen,