diff --git a/src/main/kotlin/dev/fyloz/colorrecipesexplorer/service/MixService.kt b/src/main/kotlin/dev/fyloz/colorrecipesexplorer/service/MixService.kt
index 65edbe3..8416417 100644
--- a/src/main/kotlin/dev/fyloz/colorrecipesexplorer/service/MixService.kt
+++ b/src/main/kotlin/dev/fyloz/colorrecipesexplorer/service/MixService.kt
@@ -1,8 +1,8 @@
 package dev.fyloz.colorrecipesexplorer.service
 
-import dev.fyloz.colorrecipesexplorer.exception.AlreadyExistsException
 import dev.fyloz.colorrecipesexplorer.model.*
 import dev.fyloz.colorrecipesexplorer.repository.MixRepository
+import dev.fyloz.colorrecipesexplorer.service.utils.setAll
 import org.springframework.context.annotation.Lazy
 import org.springframework.stereotype.Service
 import javax.transaction.Transactional
@@ -43,6 +43,8 @@ class MixServiceImpl(
         val mixType = mixTypeService.getOrCreateForNameAndMaterialType(entity.name, materialType)
 
         val mixMaterials = if (entity.mixMaterials != null) mixMaterialService.create(entity.mixMaterials) else setOf()
+        mixMaterialService.validateMixMaterials(mixMaterials)
+
         var mix = mix(recipe = recipe, mixType = mixType, mixMaterials = mixMaterials.toMutableSet())
         mix = save(mix)
 
@@ -68,8 +70,7 @@ class MixServiceImpl(
             }
         }
         if (entity.mixMaterials != null) {
-            mix.mixMaterials.clear()
-            mix.mixMaterials.addAll(mixMaterialService.create(entity.mixMaterials!!).toMutableSet())
+            mix.mixMaterials.setAll(mixMaterialService.create(entity.mixMaterials!!).toMutableSet())
         }
         return update(mix)
     }
diff --git a/src/main/kotlin/dev/fyloz/colorrecipesexplorer/service/RecipeStepService.kt b/src/main/kotlin/dev/fyloz/colorrecipesexplorer/service/RecipeStepService.kt
index 8fc0121..44ba176 100644
--- a/src/main/kotlin/dev/fyloz/colorrecipesexplorer/service/RecipeStepService.kt
+++ b/src/main/kotlin/dev/fyloz/colorrecipesexplorer/service/RecipeStepService.kt
@@ -31,7 +31,7 @@ class RecipeStepServiceImpl(recipeStepRepository: RecipeStepRepository) :
         if (groupInformation.steps == null) return
 
         try {
-            validateSteps(groupInformation.steps!!.toSet())
+            validateSteps(groupInformation.steps!!)
         } catch (validationException: InvalidStepsPositionsException) {
             throw InvalidGroupStepsPositionsException(groupInformation.group, validationException)
         }
diff --git a/src/test/kotlin/dev/fyloz/colorrecipesexplorer/service/MixMaterialServiceTest.kt b/src/test/kotlin/dev/fyloz/colorrecipesexplorer/service/MixMaterialServiceTest.kt
index 35259e4..bffc6a4 100644
--- a/src/test/kotlin/dev/fyloz/colorrecipesexplorer/service/MixMaterialServiceTest.kt
+++ b/src/test/kotlin/dev/fyloz/colorrecipesexplorer/service/MixMaterialServiceTest.kt
@@ -4,6 +4,7 @@ import com.nhaarman.mockitokotlin2.*
 import dev.fyloz.colorrecipesexplorer.model.*
 import dev.fyloz.colorrecipesexplorer.repository.MixMaterialRepository
 import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
 import kotlin.test.assertEquals
 import kotlin.test.assertFalse
 import kotlin.test.assertNotEquals
@@ -99,4 +100,70 @@ class MixMaterialServiceTest : AbstractModelServiceTest<MixMaterial, MixMaterial
 
         assertEquals(found.quantity, quantity)
     }
+
+    // validateMixMaterials()
+
+    @Test
+    fun `validateMixMaterials() throws InvalidMixMaterialsPositionsException when the position of the first mix material is not 1`() {
+        assertInvalidMixMaterialsPositionsException(
+          setOf(
+            mixMaterial(id = 0L, position = 0),
+            mixMaterial(id = 1L, position = 1),
+            mixMaterial(id = 2L, position = 2),
+            mixMaterial(id = 3L, position = 3)
+          ),
+          INVALID_FIRST_MIX_MATERIAL_POSITION_ERROR_CODE
+        )
+    }
+
+    @Test
+    fun `validateMixMaterials() throws InvalidMixMaterialsPositionsException when positions are duplicated`() {
+        assertInvalidMixMaterialsPositionsException(
+          setOf(
+            mixMaterial(id = 0L, position = 1),
+            mixMaterial(id = 1L, position = 2),
+            mixMaterial(id = 2L, position = 2),
+            mixMaterial(id = 3L, position = 3)
+          ),
+          DUPLICATED_MIX_MATERIALS_POSITIONS_ERROR_CODE
+        )
+    }
+
+    @Test
+    fun `validateMixMaterials() throws InvalidMixMaterialsPositionsException when there is a gap between positions`() {
+        assertInvalidMixMaterialsPositionsException(
+          setOf(
+            mixMaterial(id = 0L, position = 1),
+            mixMaterial(id = 1L, position = 2),
+            mixMaterial(id = 2L, position = 4),
+            mixMaterial(id = 3L, position = 5)
+          ),
+          GAP_BETWEEN_MIX_MATERIALS_POSITIONS_ERROR_CODE
+        )
+    }
+
+    @Test
+    fun `validateMixMaterials() throws InvalidFirstMixMaterial when the first mix material's quantity is expressed in percents`() {
+        val normalMaterial = material(materialType = materialType(usePercentages = false))
+        val percentsMaterial = material(materialType = materialType(usePercentages = true))
+        val mixMaterials = setOf(
+          mixMaterial(id = 0L, position = 1, material = percentsMaterial),
+          mixMaterial(id = 1L, position = 2, material = normalMaterial),
+          mixMaterial(id = 2L, position = 3, material = normalMaterial),
+          mixMaterial(id = 3L, position = 4, material = normalMaterial)
+        )
+
+        assertThrows<InvalidFirstMixMaterial> {
+            service.validateMixMaterials(mixMaterials)
+        }
+    }
+
+    private fun assertInvalidMixMaterialsPositionsException(mixMaterials: Set<MixMaterial>, errorType: String) {
+        val exception = assertThrows<InvalidMixMaterialsPositionsException> {
+            service.validateMixMaterials(mixMaterials)
+        }
+
+        assertTrue { exception.errors.size == 1 }
+        assertTrue { exception.errors.first().type == errorType }
+    }
 }
diff --git a/src/test/kotlin/dev/fyloz/colorrecipesexplorer/service/RecipeStepServiceTest.kt b/src/test/kotlin/dev/fyloz/colorrecipesexplorer/service/RecipeStepServiceTest.kt
index ef8d213..48f476f 100644
--- a/src/test/kotlin/dev/fyloz/colorrecipesexplorer/service/RecipeStepServiceTest.kt
+++ b/src/test/kotlin/dev/fyloz/colorrecipesexplorer/service/RecipeStepServiceTest.kt
@@ -1,7 +1,6 @@
 package dev.fyloz.colorrecipesexplorer.service
 
-import com.nhaarman.mockitokotlin2.mock
-import com.nhaarman.mockitokotlin2.spy
+import com.nhaarman.mockitokotlin2.*
 import dev.fyloz.colorrecipesexplorer.model.*
 import dev.fyloz.colorrecipesexplorer.repository.RecipeStepRepository
 import org.junit.jupiter.api.Test
@@ -19,68 +18,86 @@ class RecipeStepServiceTest :
     // validateGroupInformationSteps()
 
     @Test
-    fun `validateGroupInformationSteps() throws an InvalidGroupStepsPositionsException when the position of the first step of the given groupInformation is not 1`() {
-        withSteps(
+    fun `validateGroupInformationSteps() calls validateSteps() with the given RecipeGroupInformation steps`() {
+        withGroupInformation {
+            service.validateGroupInformationSteps(this)
+
+            verify(service).validateSteps(this.steps!!)
+        }
+    }
+
+    @Test
+    fun `validateGroupInformationSteps() throws InvalidGroupStepsPositionsException when validateSteps() throws an InvalidStepsPositionsException`() {
+        withGroupInformation {
+            doAnswer { throw InvalidStepsPositionsException(setOf()) }.whenever(service).validateSteps(this.steps!!)
+
+            assertThrows<InvalidGroupStepsPositionsException> {
+                service.validateGroupInformationSteps(this)
+            }
+        }
+    }
+
+    // validateSteps()
+
+    @Test
+    fun `validateSteps() throws an InvalidStepsPositionsException when the position of the first step of the given groupInformation is not 1`() {
+        assertInvalidStepsPositionsException(
           mutableSetOf(
             recipeStep(id = 0L, position = 0),
             recipeStep(id = 1L, position = 1),
             recipeStep(id = 2L, position = 2),
             recipeStep(id = 3L, position = 3)
-          )
-        ) {
-            val exception = assertThrows<InvalidGroupStepsPositionsException> {
-                service.validateGroupInformationSteps(this)
-            }
-
-            assertTrue { exception.errors.count() == 1 }
-            assertTrue { exception.errors.first().type == INVALID_FIRST_STEP_POSITION_ERROR_CODE }
-        }
+          ),
+          INVALID_FIRST_STEP_POSITION_ERROR_CODE
+        )
     }
 
     @Test
-    fun `validateGroupInformationSteps() throws an InvalidGroupStepsPositionsException when steps positions are duplicated in the given groupInformation`() {
-        withSteps(
+    fun `validateSteps() throws an InvalidStepsPositionsException when steps positions are duplicated in the given groupInformation`() {
+        assertInvalidStepsPositionsException(
           mutableSetOf(
             recipeStep(id = 0L, position = 1),
             recipeStep(id = 1L, position = 2),
             recipeStep(id = 2L, position = 2),
             recipeStep(id = 3L, position = 3)
-          )
-        ) {
-            val exception = assertThrows<InvalidGroupStepsPositionsException> {
-                service.validateGroupInformationSteps(this)
-            }
-
-            assertTrue { exception.errors.count() == 1 }
-            assertTrue { exception.errors.first().type == DUPLICATED_STEPS_POSITIONS_ERROR_CODE }
-        }
+          ),
+          DUPLICATED_STEPS_POSITIONS_ERROR_CODE
+        )
     }
 
     @Test
-    fun `validateGroupInformationSteps() throws an InvalidGroupStepsPositionsException when there is a gap between steps positions in the given groupInformation`() {
-        withSteps(
+    fun `validateSteps() throws an InvalidStepsPositionsException when there is a gap between steps positions in the given groupInformation`() {
+        assertInvalidStepsPositionsException(
           mutableSetOf(
             recipeStep(id = 0L, position = 1),
             recipeStep(id = 1L, position = 2),
             recipeStep(id = 2L, position = 4),
             recipeStep(id = 3L, position = 5)
-          )
-        ) {
-            val exception = assertThrows<InvalidGroupStepsPositionsException> {
-                service.validateGroupInformationSteps(this)
-            }
-
-            assertTrue { exception.errors.count() == 1 }
-            assertTrue { exception.errors.first().type == GAP_BETWEEN_STEPS_POSITIONS_ERROR_CODE }
-        }
+          ),
+          GAP_BETWEEN_STEPS_POSITIONS_ERROR_CODE
+        )
     }
 
-    private fun withSteps(steps: MutableSet<RecipeStep>, test: RecipeGroupInformation.() -> Unit) {
+    private fun withGroupInformation(steps: MutableSet<RecipeStep>? = null, test: RecipeGroupInformation.() -> Unit) {
         recipeGroupInformation(
           group = employeeGroup(id = 0L),
-          steps = steps
+          steps = steps ?: mutableSetOf(
+            recipeStep(id = 0L, position = 1),
+            recipeStep(id = 1L, position = 2),
+            recipeStep(id = 2L, position = 3),
+            recipeStep(id = 3L, position = 4)
+          )
         ) {
             test()
         }
     }
+
+    private fun assertInvalidStepsPositionsException(steps: MutableSet<RecipeStep>, errorType: String) {
+        val exception = assertThrows<InvalidStepsPositionsException> {
+            service.validateSteps(steps)
+        }
+
+        assertTrue { exception.errors.size == 1 }
+        assertTrue { exception.errors.first().type == errorType }
+    }
 }