diff -u b/core/modules/migrate/src/Plugin/migrate/process/Explode.php b/core/modules/migrate/src/Plugin/migrate/process/Explode.php
--- b/core/modules/migrate/src/Plugin/migrate/process/Explode.php
+++ b/core/modules/migrate/src/Plugin/migrate/process/Explode.php
@@ -25,9 +25,9 @@
    * {@inheritdoc}
    */
   public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
-    if (is_string($value[0])) {
+    if (is_string($value)) {
       if (!empty($this->configuration['delimiter'])) {
-        return explode($this->configuration['delimiter'], $value[0]);
+        return explode($this->configuration['delimiter'], $value);
       }
       else {
         throw new MigrateException(sprintf('delimiter is empty', var_export($value, TRUE)));
diff -u b/core/modules/migrate/tests/src/Unit/process/ExplodeTest.php b/core/modules/migrate/tests/src/Unit/process/ExplodeTest.php
--- b/core/modules/migrate/tests/src/Unit/process/ExplodeTest.php
+++ b/core/modules/migrate/tests/src/Unit/process/ExplodeTest.php
@@ -48,7 +48,7 @@
   public function testTransform() {
     $configuration['delimiter'] = '_';
     $this->plugin = new Explode($configuration, 'explode', [], $this->moduleHandler->reveal(), $this->migrationPlugin->reveal());
-    $source = ['color_bartik_stylesheets'];
+    $source = 'color_bartik_stylesheets';
     $result = ['color', 'bartik', 'stylesheets'];
     $transformed_value = $this->plugin->transform($source, $this->migrateExecutable, $this->row, 'destinationproperty');
     $this->assertSame($result, $transformed_value);
@@ -63,7 +63,7 @@
   public function testSourceString() {
     $configuration['delimiter'] = '_';
     $this->plugin = new Explode($configuration, 'explode', [], $this->moduleHandler->reveal(), $this->migrationPlugin->reveal());
-    $this->plugin->transform([ ['color_bartik_stylesheets'] ], $this->migrateExecutable, $this->row, 'destinationproperty');
+    $this->plugin->transform(['color_bartik_stylesheets'], $this->migrateExecutable, $this->row, 'destinationproperty');
   }
 
   /**
@@ -75,7 +75,7 @@
   public function testDelimiterEmpty() {
     $configuration['delimiter'] = '';
     $this->plugin = new Explode($configuration, 'explode', [], $this->moduleHandler->reveal(), $this->migrationPlugin->reveal());
-    $this->plugin->transform(['color_bartik_stylesheets'], $this->migrateExecutable, $this->row, 'destinationproperty');
+    $this->plugin->transform('color_bartik_stylesheets', $this->migrateExecutable, $this->row, 'destinationproperty');
   }
 
 }