diff --git a/drivers/i2c/i2c-slave-testunit.c b/drivers/i2c/i2c-slave-testunit.c
index 23a11e4e9256..61f3f25de372 100644
--- a/drivers/i2c/i2c-slave-testunit.c
+++ b/drivers/i2c/i2c-slave-testunit.c
@@ -33,6 +33,7 @@ enum testunit_regs {
 
 enum testunit_flags {
 	TU_FLAG_IN_PROCESS,
+	TU_FLAG_NACK,
 };
 
 struct testunit_data {
@@ -95,8 +96,10 @@ static int i2c_slave_testunit_slave_cb(struct i2c_client *client,
 
 	switch (event) {
 	case I2C_SLAVE_WRITE_RECEIVED:
-		if (test_bit(TU_FLAG_IN_PROCESS, &tu->flags))
-			return -EBUSY;
+		if (test_bit(TU_FLAG_IN_PROCESS | TU_FLAG_NACK, &tu->flags)) {
+			ret = -EBUSY;
+			break;
+		}
 
 		if (tu->reg_idx < TU_NUM_REGS)
 			tu->regs[tu->reg_idx] = *val;
@@ -125,11 +128,15 @@ static int i2c_slave_testunit_slave_cb(struct i2c_client *client,
 		 * here because we still need them in the workqueue!
 		 */
 		tu->reg_idx = 0;
+
+		clear_bit(TU_FLAG_NACK, &tu->flags);
 		break;
 
 	case I2C_SLAVE_WRITE_REQUESTED:
-		if (test_bit(TU_FLAG_IN_PROCESS, &tu->flags))
-			return -EBUSY;
+		if (test_bit(TU_FLAG_IN_PROCESS | TU_FLAG_NACK, &tu->flags)) {
+			ret = -EBUSY;
+			break;
+		}
 
 		memset(tu->regs, 0, TU_NUM_REGS);
 		tu->reg_idx = 0;
@@ -145,6 +152,10 @@ static int i2c_slave_testunit_slave_cb(struct i2c_client *client,
 		break;
 	}
 
+	/* If an error occurred somewhen, we NACK everything until next STOP */
+	if (ret)
+		set_bit(TU_FLAG_NACK, &tu->flags);
+
 	return ret;
 }