diff --git a/lib/runner.php b/lib/runner.php
index 4250b23a..22ce5821 100644
--- a/lib/runner.php
+++ b/lib/runner.php
@@ -5,6 +5,9 @@
 use phpDocumentor\Reflection\BaseReflector;
 use phpDocumentor\Reflection\ClassReflector\MethodReflector;
 use phpDocumentor\Reflection\ClassReflector\PropertyReflector;
+use phpDocumentor\Reflection\DocBlock\Context;
+use phpDocumentor\Reflection\DocBlock\Tag\MethodTag;
+use phpDocumentor\Reflection\DocBlock\Type\Collection;
 use phpDocumentor\Reflection\FunctionReflector;
 use phpDocumentor\Reflection\FunctionReflector\ArgumentReflector;
 use phpDocumentor\Reflection\ReflectionAbstract;
@@ -221,6 +224,138 @@ function ( $matches ) use ( $replacement_string ) {
 	return $text;
 }
 
+/**
+ * Splits a type expression on a delimiter outside of brackets.
+ *
+ * @param string $type      Type expression.
+ * @param string $delimiter Delimiter on which to split.
+ *
+ * @return string[]
+ */
+function split_docblock_type_expression( $type, $delimiter ) {
+	$closing_brackets = array(
+		'<' => '>',
+		'(' => ')',
+		'[' => ']',
+		'{' => '}',
+	);
+	$bracket_stack    = array();
+	$parts            = array();
+	$part             = '';
+	$length           = strlen( $type );
+
+	for ( $i = 0; $i < $length; $i++ ) {
+		$character = $type[ $i ];
+
+		if ( isset( $closing_brackets[ $character ] ) ) {
+			$bracket_stack[] = $closing_brackets[ $character ];
+		} elseif (
+			! empty( $bracket_stack )
+			&& $character === $bracket_stack[ count( $bracket_stack ) - 1 ]
+		) {
+			array_pop( $bracket_stack );
+		}
+
+		if ( $character === $delimiter && empty( $bracket_stack ) ) {
+			$parts[] = $part;
+			$part    = '';
+			continue;
+		}
+
+		$part .= $character;
+	}
+
+	$parts[] = $part;
+
+	return $parts;
+}
+
+/**
+ * Expands aliases in a type expression without losing nested type syntax.
+ *
+ * @param string       $type    Type expression.
+ * @param Context|null $context DocBlock namespace and alias context.
+ *
+ * @return string
+ */
+function expand_docblock_type_expression( $type, ?Context $context ) {
+	$type = trim( $type );
+	if ( '' === $type ) {
+		return '';
+	}
+
+	foreach ( array( '|', ',' ) as $delimiter ) {
+		$parts = split_docblock_type_expression( $type, $delimiter );
+		if ( 1 < count( $parts ) ) {
+			$expanded_parts = array();
+			foreach ( $parts as $part ) {
+				$expanded_part = expand_docblock_type_expression( $part, $context );
+				if ( '' !== $expanded_part ) {
+					$expanded_parts[] = $expanded_part;
+				}
+			}
+
+			return implode( $delimiter, $expanded_parts );
+		}
+	}
+
+	if ( '[]' === substr( $type, -2 ) ) {
+		return expand_docblock_type_expression( substr( $type, 0, -2 ), $context ) . '[]';
+	}
+
+	if ( preg_match( '/^([^<]+)<(.*)>$/s', $type, $matches ) ) {
+		$container = expand_docblock_type_expression( $matches[1], $context );
+		$arguments = expand_docblock_type_expression( $matches[2], $context );
+
+		return $container . '<' . $arguments . '>';
+	}
+
+	// `list` is a PHPDoc built-in missing from the legacy dependency's keyword list.
+	if ( 'list' === strtolower( $type ) ) {
+		return $type;
+	}
+
+	$types = new Collection( array( $type ), $context );
+
+	return isset( $types[0] ) ? $types[0] : '';
+}
+
+/**
+ * Returns context-aware types from a type-bearing DocBlock tag.
+ *
+ * @param object       $tag     DocBlock tag.
+ * @param Context|null $context DocBlock namespace and alias context.
+ *
+ * @return string[]
+ */
+function export_docblock_types( $tag, ?Context $context ) {
+	// Method tags have a distinct content grammar which may begin with `static`.
+	if ( $tag instanceof MethodTag ) {
+		return $tag->getTypes();
+	}
+
+	$content = trim( $tag->getContent() );
+	if ( '' === $content ) {
+		return $tag->getTypes();
+	}
+
+	$content_parts = preg_split( '/\s+/', $content, 2 );
+	$type          = $content_parts[0];
+	if ( '' === $type || '$' === $type[0] || '...$' === substr( $type, 0, 4 ) ) {
+		return $tag->getTypes();
+	}
+
+	$types = array();
+	foreach ( split_docblock_type_expression( $type, '|' ) as $type_part ) {
+		$expanded_type = expand_docblock_type_expression( $type_part, $context );
+		if ( '' !== $expanded_type ) {
+			$types[] = $expanded_type;
+		}
+	}
+
+	return empty( $types ) ? $tag->getTypes() : $types;
+}
+
 /**
  * @param BaseReflector|ReflectionAbstract $element
  *
@@ -248,7 +383,7 @@ function export_docblock( $element ) {
 			'content' => preg_replace( '/[\n\r]+/', ' ', format_description( $tag->getDescription() ) ),
 		);
 		if ( method_exists( $tag, 'getTypes' ) ) {
-			$tag_data['types'] = $tag->getTypes();
+			$tag_data['types'] = export_docblock_types( $tag, $docblock->getContext() );
 		}
 		if ( method_exists( $tag, 'getLink' ) ) {
 			$tag_data['link'] = $tag->getLink();
diff --git a/tests/phpunit/tests/export/docblocks.inc b/tests/phpunit/tests/export/docblocks.inc
index 05686f51..29acd460 100644
--- a/tests/phpunit/tests/export/docblocks.inc
+++ b/tests/phpunit/tests/export/docblocks.inc
@@ -10,6 +10,8 @@
  * @since 1.5.0
  */
 
+use WordPress\AiClient\Messages\DTO\MessagePart;
+
 /**
  * This is a function docblock.
  *
@@ -28,6 +30,14 @@ function test_func( $var, $num ) {
 	return true;
 }
 
+/**
+ * Tests a nested union type inside a generic.
+ *
+ * @param MessagePart|list<string|MessagePart|array>|MessagePart[] $prompt A prompt.
+ */
+function test_nested_union_type( $prompt ) {
+}
+
 /**
  * This is a class docblock.
  *
diff --git a/tests/phpunit/tests/export/docblocks.php b/tests/phpunit/tests/export/docblocks.php
index 0d49b15d..b59aa638 100644
--- a/tests/phpunit/tests/export/docblocks.php
+++ b/tests/phpunit/tests/export/docblocks.php
@@ -108,6 +108,30 @@ public function test_function_docblocks() {
 		);
 	}
 
+	/**
+	 * Test that a nested union inside a generic remains one exported type.
+	 */
+	public function test_nested_union_inside_generic() {
+
+		$this->assertFunctionHasDocs(
+			'test_nested_union_type'
+			, array(
+				'tags' => array(
+					array(
+						'name' => 'param',
+						'content' => 'A prompt.',
+						'types' => array(
+							'\WordPress\AiClient\Messages\DTO\MessagePart',
+							'list<string|\WordPress\AiClient\Messages\DTO\MessagePart|array>',
+							'\WordPress\AiClient\Messages\DTO\MessagePart[]',
+						),
+						'variable' => '$prompt',
+					),
+				),
+			)
+		);
+	}
+
 	/**
 	 * Test that class docs are exported.
 	 */