diff --git a/wp-includes/class-wp-theme-json.php b/wp-includes/class-wp-theme-json.php
index 0b94aacb59..c9517576a3 100644
--- a/wp-includes/class-wp-theme-json.php
+++ b/wp-includes/class-wp-theme-json.php
@@ -1004,6 +1004,7 @@ class WP_Theme_JSON {
 	 *
 	 * @since 5.8.0
 	 * @since 5.9.0 Removed the `$type` parameter, added the `$types` and `$origins` parameters.
+	 * @since 6.3.0 Add fallback layout styles for Post Template when block gap support isn't available.
 	 *
 	 * @param string[] $types   Types of styles to load. Will load all by default. It accepts:
 	 *                          - `variables`: only the CSS Custom Properties for presets & custom ones.
@@ -1070,11 +1071,13 @@ class WP_Theme_JSON {
 			}
 			$stylesheet .= $this->get_block_classes( $style_nodes );
 		} elseif ( in_array( 'base-layout-styles', $types, true ) ) {
-			$root_selector    = static::ROOT_BLOCK_SELECTOR;
-			$columns_selector = '.wp-block-columns';
+			$root_selector          = static::ROOT_BLOCK_SELECTOR;
+			$columns_selector       = '.wp-block-columns';
+			$post_template_selector = '.wp-block-post-template';
 			if ( ! empty( $options['scope'] ) ) {
-				$root_selector    = static::scope_selector( $options['scope'], $root_selector );
-				$columns_selector = static::scope_selector( $options['scope'], $columns_selector );
+				$root_selector          = static::scope_selector( $options['scope'], $root_selector );
+				$columns_selector       = static::scope_selector( $options['scope'], $columns_selector );
+				$post_template_selector = static::scope_selector( $options['scope'], $post_template_selector );
 			}
 			if ( ! empty( $options['root_selector'] ) ) {
 				$root_selector = $options['root_selector'];
@@ -1091,6 +1094,11 @@ class WP_Theme_JSON {
 					'selector' => $columns_selector,
 					'name'     => 'core/columns',
 				),
+				array(
+					'path'     => array( 'styles', 'blocks', 'core/post-template' ),
+					'selector' => $post_template_selector,
+					'name'     => 'core/post-template',
+				),
 			);
 
 			foreach ( $base_styles_nodes as $base_style_node ) {
@@ -1295,8 +1303,8 @@ class WP_Theme_JSON {
 			// If the block should have custom gap, add the gap styles.
 			if ( null !== $block_gap_value && false !== $block_gap_value && '' !== $block_gap_value ) {
 				foreach ( $layout_definitions as $layout_definition_key => $layout_definition ) {
-					// Allow outputting fallback gap styles for flex layout type when block gap support isn't available.
-					if ( ! $has_block_gap_support && 'flex' !== $layout_definition_key ) {
+					// Allow outputting fallback gap styles for flex and grid layout types when block gap support isn't available.
+					if ( ! $has_block_gap_support && 'flex' !== $layout_definition_key && 'grid' !== $layout_definition_key ) {
 						continue;
 					}
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 8bc43ddb78..02e427d83e 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.3-alpha-56082';
+$wp_version = '6.3-alpha-56083';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.