diff --git a/wp-includes/class-wp-query.php b/wp-includes/class-wp-query.php
index ddfd6fc7d2..e569e02ef1 100644
--- a/wp-includes/class-wp-query.php
+++ b/wp-includes/class-wp-query.php
@@ -4164,6 +4164,10 @@ class WP_Query {
 			$content = str_replace( "\n<!--nextpage-->", '<!--nextpage-->', $content );
 			$content = str_replace( "<!--nextpage-->\n", '<!--nextpage-->', $content );
 
+			// Remove the nextpage block delimiters, to avoid invalid block structures in the split content.
+			$content = str_replace( '<!-- wp:nextpage -->', '', $content );
+			$content = str_replace( '<!-- /wp:nextpage -->', '', $content );
+
 			// Ignore nextpage at the beginning of the content.
 			if ( 0 === strpos( $content, '<!--nextpage-->' ) ) {
 				$content = substr( $content, 15 );
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 17adb51f56..6cbbb289ff 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44275';
+$wp_version = '5.1-alpha-44276';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.