diff --git a/src/wp-includes/html-api/class-wp-html-processor.php b/src/wp-includes/html-api/class-wp-html-processor.php
index 14cb296d43..bba7ed5f48 100644
--- a/src/wp-includes/html-api/class-wp-html-processor.php
+++ b/src/wp-includes/html-api/class-wp-html-processor.php
@@ -557,6 +557,10 @@ class WP_HTML_Processor extends WP_HTML_Tag_Processor {
 			return false;
 		}
 
+		if ( isset( $query['tag_name'] ) ) {
+			$query['tag_name'] = strtoupper( $query['tag_name'] );
+		}
+
 		$needs_class = ( isset( $query['class_name'] ) && is_string( $query['class_name'] ) )
 			? $query['class_name']
 			: null;
diff --git a/tests/phpunit/tests/html-api/wpHtmlProcessor.php b/tests/phpunit/tests/html-api/wpHtmlProcessor.php
index 792f297142..1ece27c9db 100644
--- a/tests/phpunit/tests/html-api/wpHtmlProcessor.php
+++ b/tests/phpunit/tests/html-api/wpHtmlProcessor.php
@@ -882,4 +882,19 @@ class Tests_HtmlApi_WpHtmlProcessor extends WP_UnitTestCase {
 		$this->assertSame( 'FORM', $processor->get_tag() );
 		$this->assertTrue( $processor->is_tag_closer() );
 	}
+
+	/**
+	 * Ensure that lowercased tag_name query matches tags case-insensitively.
+	 *
+	 * @group 62427
+	 */
+	public function test_next_tag_lowercase_tag_name() {
+		// The upper case <DIV> is irrelevant but illustrates the case-insentivity.
+		$processor = WP_HTML_Processor::create_fragment( '<section><DIV>' );
+		$this->assertTrue( $processor->next_tag( array( 'tag_name' => 'div' ) ) );
+
+		// The upper case <RECT> is irrelevant but illustrates the case-insentivity.
+		$processor = WP_HTML_Processor::create_fragment( '<svg><RECT>' );
+		$this->assertTrue( $processor->next_tag( array( 'tag_name' => 'rect' ) ) );
+	}
 }