diff --git a/src/wp-includes/wp-db.php b/src/wp-includes/wp-db.php
index 02d852683e..e52d6fd2f4 100644
--- a/src/wp-includes/wp-db.php
+++ b/src/wp-includes/wp-db.php
@@ -2414,7 +2414,7 @@ class wpdb {
 		}
 
 		// Skip this entirely if this isn't a MySQL database.
-		if ( false === $this->is_mysql ) {
+		if ( empty( $this->is_mysql ) ) {
 			return false;
 		}
 
@@ -2463,7 +2463,7 @@ class wpdb {
 		$columnkey = strtolower( $column );
 
 		// Skip this entirely if this isn't a MySQL database.
-		if ( false === $this->is_mysql ) {
+		if ( empty( $this->is_mysql ) ) {
 			return false;
 		}
 
diff --git a/tests/phpunit/includes/utils.php b/tests/phpunit/includes/utils.php
index a7aec495f9..baebfe0303 100644
--- a/tests/phpunit/includes/utils.php
+++ b/tests/phpunit/includes/utils.php
@@ -380,6 +380,7 @@ class wpdb_exposed_methods_for_testing extends wpdb {
 		global $wpdb;
 		$this->dbh = $wpdb->dbh;
 		$this->use_mysqli = $wpdb->use_mysqli;
+		$this->is_mysql = $wpdb->is_mysql;
 		$this->ready = true;
 		$this->field_types = $wpdb->field_types;
 		$this->charset = $wpdb->charset;
diff --git a/tests/phpunit/tests/db/charset.php b/tests/phpunit/tests/db/charset.php
index 45c7978419..c1692921da 100644
--- a/tests/phpunit/tests/db/charset.php
+++ b/tests/phpunit/tests/db/charset.php
@@ -637,6 +637,32 @@ class Tests_DB_Charset extends WP_UnitTestCase {
 		self::$_wpdb->is_mysql = true;
 	}
 
+	/**
+	 * @dataProvider data_test_get_column_charset
+	 * @ticket 33501
+	 */
+	function test_get_column_charset_is_mysql_undefined( $drop, $create, $table, $columns ) {
+		self::$_wpdb->query( $drop );
+
+		if ( ! self::$_wpdb->has_cap( 'utf8mb4' ) && preg_match( '/utf8mb[34]/i', $create ) ) {
+			$this->markTestSkipped( "This version of MySQL doesn't support utf8mb4." );
+			return;
+		}
+
+		unset( self::$_wpdb->is_mysql );
+
+		self::$_wpdb->query( $create );
+
+		$columns = array_keys( $columns );
+		foreach ( $columns as $column => $charset ) {
+			$this->assertEquals( false, self::$_wpdb->get_col_charset( $table, $column ) );
+		}
+
+		self::$_wpdb->query( $drop );
+
+		self::$_wpdb->is_mysql = true;
+	}
+
 	/**
 	 * @ticket 21212
 	 */