diff --git a/src/wp-includes/query.php b/src/wp-includes/query.php
index b915119c35..7a210b09f1 100644
--- a/src/wp-includes/query.php
+++ b/src/wp-includes/query.php
@@ -901,6 +901,11 @@ function is_embed() {
 function is_main_query() {
 	global $wp_query;
 
+	if ( ! isset( $wp_query ) ) {
+		_doing_it_wrong( __FUNCTION__, __( 'Conditional query tags do not work before the query is run. Before then, they always return false.' ), '6.1.0' );
+		return false;
+	}
+
 	if ( 'pre_get_posts' === current_filter() ) {
 		_doing_it_wrong(
 			__FUNCTION__,
diff --git a/tests/phpunit/tests/query/conditionals.php b/tests/phpunit/tests/query/conditionals.php
index 4ef661b21a..c4f31830d6 100644
--- a/tests/phpunit/tests/query/conditionals.php
+++ b/tests/phpunit/tests/query/conditionals.php
@@ -1616,4 +1616,14 @@ class Tests_Query_Conditionals extends WP_UnitTestCase {
 		$this->assertQueryTrue( 'is_page', 'is_singular', 'is_privacy_policy' );
 	}
 
+	/**
+	 * @ticket 55104
+	 * @expectedIncorrectUsage is_main_query
+	 */
+	public function test_is_main_query_returns_false_if_wp_query_is_not_set() {
+		unset( $GLOBALS['wp_query'] );
+
+		$this->assertFalse( is_main_query() );
+	}
+
 }