diff --git a/src/main/java/es/uvigo/esei/daa/dao/PetsDAO.java b/src/main/java/es/uvigo/esei/daa/dao/PetsDAO.java
index e31c4efd3c451b9505957ab128bae143f0da9c5b..6e7fd66fd53b972fe16ce4e95183e5760fd16f4b 100644
--- a/src/main/java/es/uvigo/esei/daa/dao/PetsDAO.java
+++ b/src/main/java/es/uvigo/esei/daa/dao/PetsDAO.java
@@ -92,8 +92,16 @@ public class PetsDAO extends DAO {
 	 */
 	public Pet add(String name, String specie, int idOwner)
 	throws DAOException, IllegalArgumentException {
-		if (name == null || specie == null) {
-			throw new IllegalArgumentException("name and specie can't be null " + specie);
+		if (name == null) {
+			throw new IllegalArgumentException("name can't be null " + name);
+		}
+		
+		if ( specie == null) {
+			throw new IllegalArgumentException("specie can't be null " + specie);
+		}
+		
+		if(idOwner < 0) {
+			throw new IllegalArgumentException("idOwner can't be negative " + specie);
 		}
 				
 		try (Connection conn = this.getConnection()) {
@@ -197,7 +205,7 @@ public class PetsDAO extends DAO {
 	public List<Pet> getPets(int idOwner)
 	throws DAOException, IllegalArgumentException {
 		
-		if ( idOwner <= 0) {
+		if ( idOwner < 0) {
 			throw new IllegalArgumentException("idOwner can't be negative");
 		}
 		
diff --git a/src/main/java/es/uvigo/esei/daa/entities/Pet.java b/src/main/java/es/uvigo/esei/daa/entities/Pet.java
index 84bc5381053c494412733c3e564a703f090c6296..69b5d1e291082e38ba3a0233a538883428b10cbe 100644
--- a/src/main/java/es/uvigo/esei/daa/entities/Pet.java
+++ b/src/main/java/es/uvigo/esei/daa/entities/Pet.java
@@ -2,6 +2,7 @@ package es.uvigo.esei.daa.entities;
 
 import static java.util.Objects.requireNonNull;
 
+
 /**
  * An entity that represents a pet.
  * 
@@ -89,7 +90,10 @@ public class Pet {
 	 * @throws NullPointerException if the {@code idOwner} is {@code null}.
 	 */
 	public void setIdOwner(int idOwner) {
-		this.idOwner = requireNonNull(idOwner, "idOwner can't be null");
+		if(idOwner < 1) {
+			throw new IllegalArgumentException(idOwner + " can't be less than 0");
+		}
+		this.idOwner = idOwner;
 	}
 
 	@Override
diff --git a/src/test/java/es/uvigo/esei/daa/dao/PetsDAOTest.java b/src/test/java/es/uvigo/esei/daa/dao/PetsDAOTest.java
index 713213c53d1bedc42127f44dd9e9a0f6f91ca58a..0caf492d2d307131181b04258ade4b7c5142580a 100644
--- a/src/test/java/es/uvigo/esei/daa/dao/PetsDAOTest.java
+++ b/src/test/java/es/uvigo/esei/daa/dao/PetsDAOTest.java
@@ -9,6 +9,7 @@ import static es.uvigo.esei.daa.dataset.PetsDataset.newSpecie;
 import static es.uvigo.esei.daa.dataset.PetsDataset.newIdOwner;
 import static es.uvigo.esei.daa.dataset.PetsDataset.nonExistentId;
 import static es.uvigo.esei.daa.dataset.PetsDataset.nonExistentIdOwner;
+import static es.uvigo.esei.daa.dataset.PetsDataset.negativeIdOwner;
 import static es.uvigo.esei.daa.dataset.PetsDataset.nonExistentPet;
 import static es.uvigo.esei.daa.dataset.PetsDataset.pets;
 import static es.uvigo.esei.daa.dataset.PetsDataset.petsOwner;
@@ -72,6 +73,11 @@ public class PetsDAOTest {
 		assertThat(this.dao.getPets(existentIdOwner()), containsPetsInAnyOrder(petsOwner(existentIdOwner())));
 	}
 	
+	@Test(expected = IllegalArgumentException.class)
+	public void testGetPetsNegativeIdOwner() throws DAOException {
+		this.dao.getPets(negativeIdOwner());
+	}
+	
 	@Test
 	public void testGet() throws DAOException {
 		final Pet pet = this.dao.get(existentId());
@@ -83,7 +89,7 @@ public class PetsDAOTest {
 	public void testGetNonExistentId() throws DAOException {
 		this.dao.get(nonExistentId());
 	}
-
+	
 	@Test
 	@ExpectedDatabase("/datasets/dataset-delete-pets.xml")
 	public void testDelete() throws DAOException {
@@ -140,7 +146,12 @@ public class PetsDAOTest {
 	}
 
 	@Test(expected = IllegalArgumentException.class)
-	public void testAddNullSurname() throws DAOException {
+	public void testAddNullSpecie() throws DAOException {
 		this.dao.add(newName(), null, newIdOwner());
 	}
+	
+	@Test(expected = IllegalArgumentException.class)
+	public void testAddNegativeIdOwner() throws DAOException {
+		this.dao.add(newName(), newSpecie(),negativeIdOwner());
+	}
 }
diff --git a/src/test/java/es/uvigo/esei/daa/dataset/PetsDataset.java b/src/test/java/es/uvigo/esei/daa/dataset/PetsDataset.java
index b3d20f36402f8467e9c0497ede9b2c4745dad3a0..79f8fee4465b912b6d487597dde2f2242e11ca2f 100644
--- a/src/test/java/es/uvigo/esei/daa/dataset/PetsDataset.java
+++ b/src/test/java/es/uvigo/esei/daa/dataset/PetsDataset.java
@@ -72,6 +72,10 @@ public class PetsDataset {
 		return 1234;
 	}
 	
+	public static int negativeIdOwner() {
+		return -1;
+	}
+	
 	public static Pet existentPet() {
 		return pet(existentId());
 	}
diff --git a/src/test/java/es/uvigo/esei/daa/entities/PetUnitTest.java b/src/test/java/es/uvigo/esei/daa/entities/PetUnitTest.java
index e47452851740c79969ce8d3d8a34bfa179bb6a31..a2f64530414ffc4e48bcb48409364837dbcb70d5 100644
--- a/src/test/java/es/uvigo/esei/daa/entities/PetUnitTest.java
+++ b/src/test/java/es/uvigo/esei/daa/entities/PetUnitTest.java
@@ -36,10 +36,10 @@ public class PetUnitTest {
 		new Pet(1, "Rex", null, 1);
 	}
 	
-//	@Test(expected = Error.class)
-//	public void testPetIntStringStringIntNullidOwner() {
-//		new Pet(1, "Rex", "Dog", null);
-//	}
+	@Test(expected = IllegalArgumentException.class)
+	public void testPetIntStringStringIntNegativeIdOwner() {
+		new Pet(1, "Rex", "Dog", -1);
+	}
 	
 	@Test
 	public void testSetName() {
@@ -100,12 +100,12 @@ public class PetUnitTest {
 		assertThat(pet.getIdOwner(), is(equalTo(1)));
 	}
 	
-//	@Test(expected = Error.class)
-//	public void testSetNullIdOwner() {
-//		final Pet pet = new Pet(1, "Rex", "Dog", null);
-//		
-//		pet.setSpecie(null);
-//	}	
+	@Test(expected = IllegalArgumentException.class)
+	public void testSetNegativeIdOwner() {
+		final Pet pet = new Pet(1, "Rex", "Dog", 1);
+		
+		pet.setIdOwner(-1);
+	}	
 	
 	
 	@Test