diff --git a/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php b/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php
index 7591252b5148..2cb6eb1c8da3 100644
--- a/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php
+++ b/src/Illuminate/Database/Eloquent/Concerns/HasAttributes.php
@@ -537,7 +537,9 @@ public function getAttributeValue($key)
      */
     protected function getAttributeFromArray($key)
     {
-        return $this->getAttributes()[$key] ?? null;
+        $this->mergeAttributeFromCachedCasts($key);
+
+        return $this->attributes[$key] ?? null;
     }
 
     /**
@@ -1896,6 +1898,17 @@ protected function mergeAttributesFromCachedCasts()
         $this->mergeAttributesFromAttributeCasts();
     }
 
+    /**
+     * Merge the a cast class and attribute cast attribute back into the model.
+     *
+     * @return void
+     */
+    protected function mergeAttributeFromCachedCasts(string $key)
+    {
+        $this->mergeAttributeFromClassCasts($key);
+        $this->mergeAttributeFromAttributeCasts($key);
+    }
+
     /**
      * Merge the cast class attributes back into the model.
      *
@@ -1904,15 +1917,26 @@ protected function mergeAttributesFromCachedCasts()
     protected function mergeAttributesFromClassCasts()
     {
         foreach ($this->classCastCache as $key => $value) {
-            $caster = $this->resolveCasterClass($key);
+            $this->mergeAttributeFromClassCasts($key);
+        }
+    }
 
-            $this->attributes = array_merge(
-                $this->attributes,
-                $caster instanceof CastsInboundAttributes
-                    ? [$key => $value]
-                    : $this->normalizeCastClassResponse($key, $caster->set($this, $key, $value, $this->attributes))
-            );
+    private function mergeAttributeFromClassCasts(string $key): void
+    {
+        if (! isset($this->classCastCache[$key])) {
+            return;
         }
+
+        $value = $this->classCastCache[$key];
+
+        $caster = $this->resolveCasterClass($key);
+
+        $this->attributes = array_merge(
+            $this->attributes,
+            $caster instanceof CastsInboundAttributes
+                ? [$key => $value]
+                : $this->normalizeCastClassResponse($key, $caster->set($this, $key, $value, $this->attributes))
+        );
     }
 
     /**
@@ -1923,23 +1947,34 @@ protected function mergeAttributesFromClassCasts()
     protected function mergeAttributesFromAttributeCasts()
     {
         foreach ($this->attributeCastCache as $key => $value) {
-            $attribute = $this->{Str::camel($key)}();
+            $this->mergeAttributeFromAttributeCasts($key);
+        }
+    }
 
-            if ($attribute->get && ! $attribute->set) {
-                continue;
-            }
+    private function mergeAttributeFromAttributeCasts(string $key): void
+    {
+        if (! isset($this->attributeCastCache[$key])) {
+            return;
+        }
 
-            $callback = $attribute->set ?: function ($value) use ($key) {
-                $this->attributes[$key] = $value;
-            };
+        $value = $this->attributeCastCache[$key];
 
-            $this->attributes = array_merge(
-                $this->attributes,
-                $this->normalizeCastClassResponse(
-                    $key, $callback($value, $this->attributes)
-                )
-            );
+        $attribute = $this->{Str::camel($key)}();
+
+        if ($attribute->get && ! $attribute->set) {
+            return;
         }
+
+        $callback = $attribute->set ?: function ($value) use ($key) {
+            $this->attributes[$key] = $value;
+        };
+
+        $this->attributes = array_merge(
+            $this->attributes,
+            $this->normalizeCastClassResponse(
+                $key, $callback($value, $this->attributes)
+            )
+        );
     }
 
     /**
diff --git a/tests/Integration/Database/DatabaseEloquentModelCustomCastingTest.php b/tests/Integration/Database/DatabaseEloquentModelCustomCastingTest.php
index e9a4fbab68e4..4a7825f62d86 100644
--- a/tests/Integration/Database/DatabaseEloquentModelCustomCastingTest.php
+++ b/tests/Integration/Database/DatabaseEloquentModelCustomCastingTest.php
@@ -287,6 +287,16 @@ public function testSetToUndefinedCast()
 
         $model->undefined_cast_column = 'Glāžšķūņu rūķīši';
     }
+
+    public function testMutatorCanDependOnAnotherCastedAttribute()
+    {
+        $model = new TestEloquentModelWithCustomCast([
+            'address_line_one' => '110 Kingsbrook St.',
+            'address_line_two' => 'My Childhood House',
+        ]);
+        $model->address->lineOne = 'Changed St.';
+        $this->assertSame('Changed St. (My Childhood House)', $model->address_string);
+    }
 }
 
 class TestEloquentModelWithCustomCast extends Model
@@ -319,6 +329,26 @@ class TestEloquentModelWithCustomCast extends Model
         'anniversary_on_with_object_caching' => DateTimezoneCasterWithObjectCaching::class.':America/New_York',
         'anniversary_on_without_object_caching' => DateTimezoneCasterWithoutObjectCaching::class.':America/New_York',
     ];
+
+    /**
+     * A computed attribute that depends on another casted attribute.
+     *
+     * This simulates a mutator that uses the value of a casted property.
+     */
+    protected function addressString(): \Illuminate\Database\Eloquent\Casts\Attribute
+    {
+        return \Illuminate\Database\Eloquent\Casts\Attribute::get(function () {
+            $address = $this->address;
+
+            // If mergeAttributesFromClassCasts() hasn't prepared casts properly,
+            // this could be an array instead of an Address instance.
+            if (! $address instanceof Address) {
+                throw new \RuntimeException('Address was not cast before mutator access.');
+            }
+
+            return "{$address->lineOne} ({$address->lineTwo})";
+        });
+    }
 }
 
 class HashCaster implements CastsInboundAttributes
diff --git a/tests/Integration/Database/EloquentModelEncryptedCastingTest.php b/tests/Integration/Database/EloquentModelEncryptedCastingTest.php
index 0c87c7440022..7c637a756cba 100644
--- a/tests/Integration/Database/EloquentModelEncryptedCastingTest.php
+++ b/tests/Integration/Database/EloquentModelEncryptedCastingTest.php
@@ -189,7 +189,7 @@ public function testAsEncryptedCollection()
             ->with('{"key1":"value1"}')
             ->andReturn('encrypted-secret-collection-string-1');
         $this->encrypter->expects('encryptString')
-            ->times(10)
+            ->times(9)
             ->with('{"key1":"value1","key2":"value2"}')
             ->andReturn('encrypted-secret-collection-string-2');
         $this->encrypter->expects('decryptString')
@@ -239,7 +239,7 @@ public function testAsEncryptedCollectionMap()
             ->with('[{"key1":"value1"}]')
             ->andReturn('encrypted-secret-collection-string-1');
         $this->encrypter->expects('encryptString')
-            ->times(12)
+            ->times(11)
             ->with('[{"key1":"value1"},{"key2":"value2"}]')
             ->andReturn('encrypted-secret-collection-string-2');
         $this->encrypter->expects('decryptString')
@@ -295,7 +295,7 @@ public function testAsEncryptedArrayObject()
             ->with('encrypted-secret-array-string-1')
             ->andReturn('{"key1":"value1"}');
         $this->encrypter->expects('encryptString')
-            ->times(10)
+            ->times(9)
             ->with('{"key1":"value1","key2":"value2"}')
             ->andReturn('encrypted-secret-array-string-2');
         $this->encrypter->expects('decryptString')