diff -u b/src/Plugin/migrate/process/CallbackArray.php b/src/Plugin/migrate/process/CallbackArray.php
--- b/src/Plugin/migrate/process/CallbackArray.php
+++ b/src/Plugin/migrate/process/CallbackArray.php
@@ -13,6 +13,11 @@
  * parameters, whereas the original Callback plugin only calls call_user_func()
  * with the source value.
  *
+ * Available configuration keys:
+ * - callable: The function name to call.
+ * - index: position where use the input value from the source.
+ * - allow_constant: To allow constant values, without it, the constants values
+ *     won't be replaced.
  * Example:
  *
  * @code
@@ -65,7 +70,10 @@
    * {@inheritdoc}
    */
   public function __construct(array $configuration, $plugin_id, $plugin_definition) {
-    $configuration += ['index' => 0];
+    $configuration += [
+      'index' => 0,
+    ];
+
     if (is_null($configuration['parameters'])) {
       throw new \InvalidArgumentException('The "parameters" must be set.');
     }
@@ -90,9 +98,14 @@
     foreach ($this->configuration['parameters'] as $parameter) {
-      $parameters[] = $row->get($parameter) ? $row->get($parameter) : $parameter;
+      $parameter = $row->get($parameter) ? $row->get($parameter) : $parameter;
+
+      // Allow the use of PHP constants.
+      if (isset($this->configuration['allow_constant']) && defined($parameter)) {
+        $parameter = constant($parameter);
+      }
+      $parameters[] = $parameter;
     }
 
     array_splice($parameters, $this->configuration['index'], 0, [$value]);
     return call_user_func_array($this->configuration['callable'], $parameters);
   }
-
 }
diff -u b/tests/src/Unit/process/CallbackArrayTest.php b/tests/src/Unit/process/CallbackArrayTest.php
--- b/tests/src/Unit/process/CallbackArrayTest.php
+++ b/tests/src/Unit/process/CallbackArrayTest.php
@@ -27,6 +27,7 @@
       $this->propertyName => 'text_replaced',
       'constants' => [
         'type' => 'example_type',
+        'sort_regular' => 'SORT_REGULAR'
       ],
     ]);
   }
@@ -39,7 +40,8 @@
     $configuration = [
       'parameters' => NULL,
     ];
-    $this->setExpectedException(InvalidArgumentException::class, 'The "parameters" must be set.');
+    $this->expectException(InvalidArgumentException::class);
+    $this->expectExceptionMessage('The "parameters" must be set.');
     new CallbackArray($configuration, 'callback_array', []);
   }
 
@@ -50,7 +52,8 @@
     $configuration = [
       'parameters' => 'bad way',
     ];
-    $this->setExpectedException(InvalidArgumentException::class, 'The "parameters" must be a non-empty array.');
+    $this->expectException(InvalidArgumentException::class);
+    $this->expectExceptionMessage('The "parameters" must be a non-empty array.');
     new CallbackArray($configuration, 'callback_array', []);
   }
 
@@ -64,7 +67,8 @@
       ],
       'index' => 2,
     ];
-    $this->setExpectedException(InvalidArgumentException::class, 'The "index" may not exceed the amount of "parameters".');
+    $this->expectException(InvalidArgumentException::class);
+    $this->expectExceptionMessage('The "index" may not exceed the amount of "parameters".');
     new CallbackArray($configuration, 'callback_array', []);
   }
 
@@ -92,6 +96,54 @@
   }
 
   /**
+   * Test the transform method with constant values.
+   */
+  public function testTransformWithConstant() {
+
+    // Base case using strings.
+    $value = ["a" => "2", "red", 1 => 2, "blue", "red"];
+    $expected = ['a' => '2', 0 => 'red', 1 => 2, 2 => 'blue'];
+
+    $configuration = [
+      'callable' => 'array_unique',
+      'index' => 0,
+      'allow_constant' => '1',
+      'parameters' => [
+        'SORT_REGULAR',
+      ],
+    ];
+
+    $this->plugin = new CallbackArray($configuration, 'callback_array', []);
+    $value = $this->plugin->transform($value, $this->migrateExecutable, $this->row, 'destinationproperty');
+    $this->assertSame($expected, $value);
+  }
+
+  /**
+   * Test the transform method with constant values.
+   */
+  public function testTransformWithoutConstant() {
+
+    $value = ["a" => "2", "red", 1 => 2, "blue", "red"];
+    $configuration = [
+      'callable' => 'array_unique',
+      'index' => 0,
+      'parameters' => [
+        'SORT_REGULAR',
+      ],
+    ];
+
+    // SORT_REGULAR as string is not a valid value for array_unique.
+    $this->plugin = new CallbackArray($configuration, 'callback_array', []);
+    try {
+      $this->plugin->transform($value, $this->migrateExecutable, $this->row, 'destinationproperty');
+    }
+    catch (\Exception $e) {
+      $this->assertEquals('array_unique() expects parameter 2 to be int, string given', $e->getMessage());
+    }
+
+  }
+
+  /**
    * Test the transform method using params as inputs.
    */
   public function testTransformWithSourceParams() {