diff --git a/examples/iscsi-dd.c b/examples/iscsi-dd.c
index 01eee75..7dfae04 100644
--- a/examples/iscsi-dd.c
+++ b/examples/iscsi-dd.c
@@ -96,7 +96,7 @@ void read10_cb(struct iscsi_context *iscsi _U_, int status, void *command_data,
 	wt->rt = task;
 	wt->client = client;
 
-	read10_cdb = scsi_cdb_unmarshall(task);
+	read10_cdb = scsi_cdb_unmarshall(task, SCSI_OPCODE_READ10);
 	if (read10_cdb == NULL) {
 		printf("Failed to unmarshall READ10 CDB.\n");
 		exit(10);
diff --git a/include/scsi-lowlevel.h b/include/scsi-lowlevel.h
index 6d2a086..0e1a78e 100644
--- a/include/scsi-lowlevel.h
+++ b/include/scsi-lowlevel.h
@@ -671,7 +671,7 @@ struct scsi_read10_cdb {
 
 EXTERN int scsi_datain_getfullsize(struct scsi_task *task);
 EXTERN void *scsi_datain_unmarshall(struct scsi_task *task);
-EXTERN void *scsi_cdb_unmarshall(struct scsi_task *task);
+EXTERN void *scsi_cdb_unmarshall(struct scsi_task *task, enum scsi_opcode opcode);
 
 EXTERN struct scsi_task *scsi_cdb_read6(uint32_t lba, uint32_t xferlen, int blocksize);
 EXTERN struct scsi_task *scsi_cdb_read10(uint32_t lba, uint32_t xferlen, int blocksize, int rdprotect, int dpo, int fua, int fua_nv, int group_number);
diff --git a/lib/scsi-lowlevel.c b/lib/scsi-lowlevel.c
index a583a2b..7a9c9b3 100644
--- a/lib/scsi-lowlevel.c
+++ b/lib/scsi-lowlevel.c
@@ -2334,8 +2334,12 @@ scsi_read10_cdb_unmarshall(struct scsi_task *task)
 }
 
 void *
-scsi_cdb_unmarshall(struct scsi_task *task)
+scsi_cdb_unmarshall(struct scsi_task *task, enum scsi_opcode opcode)
 {
+	if (task->cdb[0] != opcode) {
+		return NULL;
+	}
+
 	switch (task->cdb[0]) {
 	case SCSI_OPCODE_READ10:
 		return scsi_read10_cdb_unmarshall(task);