diff --git a/src/wp-includes/rest-api/class-wp-rest-request.php b/src/wp-includes/rest-api/class-wp-rest-request.php
index 9c5410a0ec..23156a31b0 100644
--- a/src/wp-includes/rest-api/class-wp-rest-request.php
+++ b/src/wp-includes/rest-api/class-wp-rest-request.php
@@ -451,7 +451,11 @@ class WP_REST_Request implements ArrayAccess {
 
 		$params = array();
 		foreach ( $order as $type ) {
-			$params = array_merge( $params, (array) $this->params[ $type ] );
+			// array_merge / the "+" operator will mess up
+			// numeric keys, so instead do a manual foreach.
+			foreach ( (array) $this->params[ $type ] as $key => $value ) {
+				$params[ $key ] = $value;
+			}
 		}
 
 		return $params;
diff --git a/tests/phpunit/tests/rest-api/rest-request.php b/tests/phpunit/tests/rest-api/rest-request.php
index 925853c8cd..47d4c32c8f 100644
--- a/tests/phpunit/tests/rest-api/rest-request.php
+++ b/tests/phpunit/tests/rest-api/rest-request.php
@@ -286,6 +286,18 @@ class Tests_REST_Request extends WP_UnitTestCase {
 		$this->assertEquals( $expected, $this->request->get_params() );
 	}
 
+	public function test_parameter_merging_with_numeric_keys() {
+		$this->request->set_query_params( array(
+			'1'           => 'hello',
+			'2'           => 'goodbye',
+		) );
+		$expected = array(
+			'1'           => 'hello',
+			'2'           => 'goodbye',
+		);
+		$this->assertEquals( $expected, $this->request->get_params() );
+	}
+
 	public function test_sanitize_params() {
 		$this->request->set_url_params( array(
 			'someinteger' => '123',