diff --git a/wp-admin/includes/template.php b/wp-admin/includes/template.php
index 58505fa9f4..336e353a28 100644
--- a/wp-admin/includes/template.php
+++ b/wp-admin/includes/template.php
@@ -1137,25 +1137,27 @@ function do_meta_boxes( $screen, $context, $object ) {
 						continue;
 					}
 
-					// Don't show boxes in the block editor, if they're just here for back compat.
-					if ( $screen->is_block_editor() && isset( $box['args']['__back_compat_meta_box'] ) && $box['args']['__back_compat_meta_box'] ) {
-						continue;
-					}
+					if ( is_array( $box[ 'args' ] ) ) {
+						// If a meta box is just here for back compat, don't show it in the block editor.
+						if ( $screen->is_block_editor() && isset( $box['args']['__back_compat_meta_box'] ) && $box['args']['__back_compat_meta_box'] ) {
+							continue;
+						}
 
-					// Don't show boxes in the block editor that aren't compatible with the block editor.
-					if ( $screen->is_block_editor() && isset( $box['args']['__block_editor_compatible_meta_box'] ) && ! $box['args']['__block_editor_compatible_meta_box'] ) {
-						continue;
-					}
+						// If a meta box doesn't work in the block editor, don't show it in the block editor.
+						if ( $screen->is_block_editor() && isset( $box['args']['__block_editor_compatible_meta_box'] ) && ! $box['args']['__block_editor_compatible_meta_box'] ) {
+							continue;
+						}
 
-					$block_compatible = true;
-					if ( isset( $box['args']['__block_editor_compatible_meta_box'] ) ) {
-						$block_compatible = (bool) $box['args']['__block_editor_compatible_meta_box'];
-						unset( $box['args']['__block_editor_compatible_meta_box'] );
-					}
+						$block_compatible = true;
+						if ( isset( $box['args']['__block_editor_compatible_meta_box'] ) ) {
+							$block_compatible = (bool) $box['args']['__block_editor_compatible_meta_box'];
+							unset( $box['args']['__block_editor_compatible_meta_box'] );
+						}
 
-					if ( isset( $box['args']['__back_compat_meta_box'] ) ) {
-						$block_compatible |= (bool) $box['args']['__back_compat_meta_box'];
-						unset( $box['args']['__back_compat_meta_box'] );
+						if ( isset( $box['args']['__back_compat_meta_box'] ) ) {
+							$block_compatible = $block_compatible || (bool) $box['args']['__back_compat_meta_box'];
+							unset( $box['args']['__back_compat_meta_box'] );
+						}
 					}
 
 					$i++;
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 3a0b603c76..3f346e5399 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44173';
+$wp_version = '5.1-alpha-44174';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.