diff --git a/07_errors/patrickmarabeas/mapStore.go b/07_errors/patrickmarabeas/mapStore.go
index 187bb55d3..59b9aa312 100644
--- a/07_errors/patrickmarabeas/mapStore.go
+++ b/07_errors/patrickmarabeas/mapStore.go
@@ -9,43 +9,50 @@ func NewMapStore() Storer {
 }
 
 // Create increments the uuid and adds the provided Puppy struct to the store with this identifier.
-func (store *MapStore) Create(puppy Puppy) int {
+func (store *MapStore) Create(puppy Puppy) (int, error) {
+	if puppy.Value < 0 {
+		return -1, NewError(NegativeValue)
+	}
+
 	puppy.ID = store.uuid
 	store.store[puppy.ID] = puppy
 	store.uuid++
 
-	return puppy.ID
+	return puppy.ID, nil
 }
 
 // Read returns the puppy matching the provided uuid.
 // An empty Puppy struct is returned if the identifier does not exist.
-func (store *MapStore) Read(id int) Puppy {
+func (store *MapStore) Read(id int) (Puppy, error) {
 	if _, ok := store.store[id]; ok {
-		return store.store[id]
+		return store.store[id], nil
 	}
 
-	return Puppy{}
+	return Puppy{}, NewError(IDNotFound)
 }
 
 // Update modifies the puppy matching the provided uuid in the store with the provided Puppy struct.
 // It returns a bool whether a matching identifier was modified or not.
-func (store *MapStore) Update(id int, puppy Puppy) bool {
+func (store *MapStore) Update(id int, puppy Puppy) (bool, error) {
 	if _, ok := store.store[id]; !ok {
-		return false
+		return false, NewError(IDNotFound)
+	}
+	if puppy.Value < 0 {
+		return false, NewError(NegativeValue)
 	}
 
 	puppy.ID = id
 	store.store[id] = puppy
-	return true
+	return true, nil
 }
 
 // Destroy removes the puppy matching the provided uuid from the store.
 // It returns a bool whether a matching identifier was deleted or not.
-func (store *MapStore) Destroy(id int) bool {
+func (store *MapStore) Destroy(id int) (bool, error) {
 	if _, ok := store.store[id]; !ok {
-		return false
+		return false, NewError(IDNotFound)
 	}
 
 	delete(store.store, id)
-	return true
+	return true, nil
 }
diff --git a/07_errors/patrickmarabeas/store_test.go b/07_errors/patrickmarabeas/store_test.go
index bb9899ed1..22a1c7a2e 100644
--- a/07_errors/patrickmarabeas/store_test.go
+++ b/07_errors/patrickmarabeas/store_test.go
@@ -14,70 +14,99 @@ type StoreSuite struct {
 
 func (suite *StoreSuite) TestCreate() {
 	a := assert.New(suite.T())
-	id := suite.store.Create(Puppy{Breed: "Wolf", Color: "Grey", Value: "450"})
 
+	id, error := suite.store.Create(Puppy{Breed: "Wolf", Color: "Grey", Value: 450})
 	a.Equal(id, 0)
+	a.Equal(error, nil)
 }
 
 func (suite *StoreSuite) TestCreateSecond() {
 	a := assert.New(suite.T())
-	id := suite.store.Create(Puppy{Breed: "Boxer", Color: "Brown", Value: "300"})
 
+	id, error := suite.store.Create(Puppy{Breed: "Boxer", Color: "Brown", Value: 300})
 	a.Equal(id, 1)
+	a.Equal(error, nil)
+}
+
+func (suite *StoreSuite) TestCreateNegativeNumber() {
+	a := assert.New(suite.T())
+
+	id, error := suite.store.Create(Puppy{Breed: "Wolf", Color: "Grey", Value: -100})
+	a.Equal(id, -1)
+	a.Equal(error, NewError(NegativeValue))
 }
 
 func (suite *StoreSuite) TestRead() {
 	a := assert.New(suite.T())
-	data := suite.store.Read(0)
 
-	a.Equal(data, Puppy{ID: 0, Breed: "Wolf", Color: "Grey", Value: "450"})
+	data, error := suite.store.Read(0)
+	a.Equal(data, Puppy{ID: 0, Breed: "Wolf", Color: "Grey", Value: 450})
+	a.Equal(error, nil)
 }
 
 func (suite *StoreSuite) TestReadNonExistent() {
 	a := assert.New(suite.T())
-	success := suite.store.Read(100)
 
+	success, error := suite.store.Read(100)
 	a.Equal(success, Puppy{})
+	a.Equal(error, NewError(IDNotFound))
 }
 
 func (suite *StoreSuite) TestUpdate() {
 	a := assert.New(suite.T())
-	success := suite.store.Update(0, Puppy{Breed: "Doberman", Color: "Black", Value: "500"})
-	data := suite.store.Read(0)
 
+	success, error := suite.store.Update(0, Puppy{Breed: "Doberman", Color: "Black", Value: 500})
 	a.Equal(success, true)
-	a.Equal(data, Puppy{ID: 0, Breed: "Doberman", Color: "Black", Value: "500"})
+	a.Equal(error, nil)
+
+	data, error := suite.store.Read(0)
+	a.Equal(data, Puppy{ID: 0, Breed: "Doberman", Color: "Black", Value: 500})
+	a.Equal(error, nil)
 }
 
 func (suite *StoreSuite) TestUpdateNonExistent() {
 	a := assert.New(suite.T())
-	success := suite.store.Update(100, Puppy{Breed: "Doberman", Color: "Black", Value: "500"})
 
+	success, error := suite.store.Update(100, Puppy{Breed: "Doberman", Color: "Black", Value: 500})
+	a.Equal(success, false)
+	a.Equal(error, NewError(IDNotFound))
+}
+
+func (suite *StoreSuite) TestUpdateNegativeNumber() {
+	a := assert.New(suite.T())
+
+	success, error := suite.store.Update(0, Puppy{Breed: "Doberman", Color: "Black", Value: -500})
 	a.Equal(success, false)
+	a.Equal(error, NewError(NegativeValue))
 }
 
 func (suite *StoreSuite) TestDestroy() {
 	a := assert.New(suite.T())
-	success := suite.store.Destroy(1)
-	data := suite.store.Read(1)
 
+	success, error := suite.store.Destroy(1)
 	a.Equal(success, true)
+	a.Equal(error, nil)
+
+	data, error := suite.store.Read(1)
 	a.Equal(data, Puppy{})
+	a.Equal(error, NewError(IDNotFound))
 }
 
 func (suite *StoreSuite) TestDestroyNonExistent() {
 	a := assert.New(suite.T())
-	success := suite.store.Destroy(100)
 
+	success, error := suite.store.Destroy(100)
 	a.Equal(success, false)
+	a.Equal(error, NewError(IDNotFound))
 }
 
 func (suite *StoreSuite) TestIdIncrementOnDelete() {
 	a := assert.New(suite.T())
-	id := suite.store.Create(Puppy{Breed: "Greyhound", Color: "Light Brown", Value: "700"})
-	suite.store.Destroy(id)
-	newID := suite.store.Create(Puppy{Breed: "Greyhound", Color: "Light Brown", Value: "700"})
+	id, _ := suite.store.Create(Puppy{Breed: "Greyhound", Color: "Light Brown", Value: 700})
+	success, _ := suite.store.Destroy(id)
+	a.Equal(success, true)
 
+	newID, _ := suite.store.Create(Puppy{Breed: "Greyhound", Color: "Light Brown", Value: 700})
 	a.Equal(newID, 3)
 }
 
diff --git a/07_errors/patrickmarabeas/syncStore.go b/07_errors/patrickmarabeas/syncStore.go
index 47dc770f5..12f1a529a 100644
--- a/07_errors/patrickmarabeas/syncStore.go
+++ b/07_errors/patrickmarabeas/syncStore.go
@@ -8,43 +8,50 @@ func NewSyncStore() Storer {
 }
 
 // Create increments the uuid and adds the provided Puppy struct to the store with this identifier.
-func (store *SyncStore) Create(puppy Puppy) int {
+func (store *SyncStore) Create(puppy Puppy) (int, error) {
+	if puppy.Value < 0 {
+		return -1, NewError(NegativeValue)
+	}
+
 	puppy.ID = store.uuid
 	store.Store(puppy.ID, puppy)
 	store.uuid++
 
-	return puppy.ID
+	return puppy.ID, nil
 }
 
 // Read returns the puppy matching the provided uuid.
 // An empty Puppy struct is returned if the identifier does not exist.
-func (store *SyncStore) Read(id int) Puppy {
+func (store *SyncStore) Read(id int) (Puppy, error) {
 	if value, ok := store.Load(id); ok {
-		return value.(Puppy)
+		return value.(Puppy), nil
 	}
 
-	return Puppy{}
+	return Puppy{}, NewError(IDNotFound)
 }
 
 // Update modifies the puppy matching the provided uuid in the store with the provided Puppy struct.
 // It returns a bool whether a matching identifier was modified or not.
-func (store *SyncStore) Update(id int, puppy Puppy) bool {
+func (store *SyncStore) Update(id int, puppy Puppy) (bool, error) {
 	if _, ok := store.Load(id); !ok {
-		return false
+		return false, NewError(IDNotFound)
+	}
+	if puppy.Value < 0 {
+		return false, NewError(NegativeValue)
 	}
 
 	puppy.ID = id
 	store.Store(id, puppy)
-	return true
+	return true, nil
 }
 
 // Destroy removes the puppy matching the provided uuid from the store.
 // It returns a bool whether a matching identifier was deleted or not.
-func (store *SyncStore) Destroy(id int) bool {
+func (store *SyncStore) Destroy(id int) (bool, error) {
 	if _, ok := store.Load(id); !ok {
-		return false
+		return false, NewError(IDNotFound)
 	}
 
 	store.Delete(id)
-	return true
+	return true, nil
 }