diff --git a/src/wp-includes/block-supports/layout.php b/src/wp-includes/block-supports/layout.php
index c10da1f8db04b..db96f3c56f113 100644
--- a/src/wp-includes/block-supports/layout.php
+++ b/src/wp-includes/block-supports/layout.php
@@ -497,13 +497,16 @@ function wp_register_layout_support( $block_type ) {
  * @return string CSS styles on success. Else, empty string.
  */
 function wp_get_layout_style( $selector, $layout, $has_block_gap_support = false, $gap_value = null, $should_skip_gap_serialization = false, $fallback_gap_value = '0.5em', $block_spacing = null, $options = array() ) {
-	$base_layout                    = is_array( $layout ) ? $layout : array();
-	$viewport_overrides             = $options['viewport_overrides'] ?? null;
-	$layout_for_styles              = null === $viewport_overrides ? $base_layout : array_replace( $base_layout, $viewport_overrides );
-	$layout_type                    = $base_layout['type'] ?? 'default';
-	$rules_group                    = $options['rules_group'] ?? null;
-	$has_block_gap_override         = ! empty( $options['has_block_gap_override'] );
-	$should_output_block_gap        = null === $viewport_overrides || $has_block_gap_override;
+	$base_layout             = is_array( $layout ) ? $layout : array();
+	$viewport_overrides      = $options['viewport_overrides'] ?? null;
+	$layout_for_styles       = null === $viewport_overrides ? $base_layout : array_replace( $base_layout, $viewport_overrides );
+	$layout_type             = $base_layout['type'] ?? 'default';
+	$rules_group             = $options['rules_group'] ?? null;
+	$has_block_gap_override  = ! empty( $options['has_block_gap_override'] );
+	$should_output_block_gap = null === $viewport_overrides || $has_block_gap_override;
+	// Viewport styles only store changed fields. If a field is present with null,
+	// the user cleared a value inherited from the default viewport, so check
+	// whether the key exists rather than whether the value is truthy.
 	$has_viewport_property_override = static function ( $property ) use ( $viewport_overrides ) {
 		return array_key_exists( $property, $viewport_overrides );
 	};
@@ -546,8 +549,29 @@ function wp_get_layout_style( $selector, $layout, $has_block_gap_support = false
 		$wide_size       = $layout_for_styles['wideSize'] ?? '';
 		$justify_content = $layout_for_styles['justifyContent'] ?? 'center';
 
-		$all_max_width_value  = $content_size ? $content_size : $wide_size;
-		$wide_max_width_value = $wide_size ? $wide_size : $content_size;
+		// Check if viewport-specific ("override") values exist. Null values are valid and mean the user cleared a value inherited from the default viewport.
+		$has_justify_content_override = null !== $viewport_overrides && $has_viewport_property_override( 'justifyContent' );
+		$has_content_size_override    = null !== $viewport_overrides && $has_viewport_property_override( 'contentSize' );
+		$has_wide_size_override       = null !== $viewport_overrides && $has_viewport_property_override( 'wideSize' );
+
+		/*
+		 * Styles should be output either if there are no viewport overrides (this is the default case), or if the user has set a new viewport-specific
+		 * value for contentSize or wideSize. If a viewport clears a custom constrained size, reset to the global layout variable.
+		 */
+		$should_output_constrained_sizes = null === $viewport_overrides || $has_content_size_override || $has_wide_size_override;
+		$is_resetting_constrained_sizes  = null !== $viewport_overrides &&
+			(
+				( $has_content_size_override && ! $content_size ) ||
+				( $has_wide_size_override && ! $wide_size )
+			);
+
+		// If a viewport clears a custom constrained size, reset to the global layout variable.
+		$all_max_width_value  = $content_size
+			? $content_size
+			: ( $wide_size && ! $has_content_size_override ? $wide_size : 'var(--wp--style--global--content-size, none)' );
+		$wide_max_width_value = $wide_size
+			? $wide_size
+			: ( $content_size && ! $has_wide_size_override ? $content_size : 'var(--wp--style--global--wide-size, none)' );
 
 		// Make sure there is a single CSS rule, and all tags are stripped for security.
 		$all_max_width_value  = safecss_filter_attr( explode( ';', $all_max_width_value )[0] );
@@ -556,9 +580,7 @@ function wp_get_layout_style( $selector, $layout, $has_block_gap_support = false
 		$margin_left  = 'left' === $justify_content ? '0 !important' : 'auto !important';
 		$margin_right = 'right' === $justify_content ? '0 !important' : 'auto !important';
 
-		$has_justify_content_override    = null !== $viewport_overrides && $has_viewport_property_override( 'justifyContent' );
-		$should_output_constrained_sizes = null === $viewport_overrides || $has_viewport_property_override( 'contentSize' ) || $has_viewport_property_override( 'wideSize' );
-		if ( $should_output_constrained_sizes && ( $content_size || $wide_size ) ) {
+		if ( $should_output_constrained_sizes && ( $content_size || $wide_size || $is_resetting_constrained_sizes ) ) {
 			$content_size_declarations = array(
 				'max-width' => $all_max_width_value,
 			);
@@ -698,6 +720,10 @@ function wp_get_layout_style( $selector, $layout, $has_block_gap_support = false
 			$vertical_alignment_options += array( 'space-between' => 'space-between' );
 		}
 
+		/*
+		 * Styles should be output either if there are no viewport overrides (this is the default case), or if the user has set a new viewport-specific
+		 * value for any of the flex properties.
+		 */
 		$should_output_flex_wrap          = null === $viewport_overrides || $has_viewport_property_override( 'flexWrap' );
 		$should_output_flex_orientation   = null === $viewport_overrides || $has_viewport_property_override( 'orientation' );
 		$should_output_flex_justification = null === $viewport_overrides || $has_viewport_property_override( 'justifyContent' ) || $has_viewport_property_override( 'orientation' );
@@ -828,6 +854,10 @@ function wp_get_layout_style( $selector, $layout, $has_block_gap_support = false
 			$responsive_gap_value = '0px';
 		}
 
+		/*
+		 * Styles should be output either if there are no viewport overrides (this is the default case), or if the user has set a new viewport-specific
+		 * value for any of the grid properties.
+		 */
 		$should_output_grid_columns = null === $viewport_overrides || $has_viewport_property_override( 'minimumColumnWidth' ) || $has_viewport_property_override( 'columnCount' ) || $has_viewport_property_override( 'autoFit' );
 		$uses_gap_in_grid_columns   = ! empty( $layout_for_styles['columnCount'] ) && ! empty( $layout_for_styles['minimumColumnWidth'] );
 		if ( $has_block_gap_override && $uses_gap_in_grid_columns ) {
@@ -837,8 +867,10 @@ function wp_get_layout_style( $selector, $layout, $has_block_gap_support = false
 		$should_output_grid_rows = ( null === $viewport_overrides || $has_viewport_property_override( 'rowCount' ) ) && ! empty( $layout_for_styles['columnCount'] ) && ! empty( $layout_for_styles['rowCount'] );
 		$grid_declarations       = array();
 
-		// When enabled, columns stretch to fill the available space using
-		// `auto-fit`; otherwise empty tracks are preserved with `auto-fill`.
+		/*
+		 * When enabled, columns stretch to fill the available space using
+		 * `auto-fit`; otherwise empty tracks are preserved with `auto-fill`.
+		 */
 		$auto_placement = ! empty( $layout_for_styles['autoFit'] ) ? 'auto-fit' : 'auto-fill';
 
 		if ( $should_output_grid_columns && ! empty( $layout_for_styles['columnCount'] ) && ! empty( $layout_for_styles['minimumColumnWidth'] ) ) {
diff --git a/tests/phpunit/tests/block-supports/wpGetLayoutStyle.php b/tests/phpunit/tests/block-supports/wpGetLayoutStyle.php
index 190170be1d933..4088a260fc157 100644
--- a/tests/phpunit/tests/block-supports/wpGetLayoutStyle.php
+++ b/tests/phpunit/tests/block-supports/wpGetLayoutStyle.php
@@ -13,6 +13,7 @@ class Tests_Block_Supports_WpGetLayoutStyle extends WP_UnitTestCase {
 		'should_skip_gap_serialization' => false,
 		'fallback_gap_value'            => '0.5em',
 		'block_spacing'                 => null,
+		'options'                       => array(),
 	);
 
 	/**
@@ -32,7 +33,8 @@ public function test_wp_get_layout_style( array $args, $expected_output ) {
 			$args['gap_value'],
 			$args['should_skip_gap_serialization'],
 			$args['fallback_gap_value'],
-			$args['block_spacing']
+			$args['block_spacing'],
+			$args['options']
 		);
 
 		$this->assertSame( $expected_output, $layout_styles );
@@ -120,6 +122,21 @@ public function data_wp_get_layout_style() {
 				),
 				'expected_output' => '.wp-layout > :where(:not(.alignleft):not(.alignright):not(.alignfull)){max-width:800px;margin-left:auto !important;margin-right:auto !important;}.wp-layout > .alignwide{max-width:1200px;}.wp-layout .alignfull{max-width:none;}.wp-layout > .alignfull{margin-right:calc(10px * -1);margin-left:calc(20px * -1);}',
 			),
+			'constrained layout with content size unset in viewport' => array(
+				'args'            => array(
+					'selector' => '.wp-layout',
+					'layout'   => array(
+						'type'        => 'constrained',
+						'contentSize' => '800px',
+					),
+					'options'  => array(
+						'viewport_overrides' => array(
+							'contentSize' => null,
+						),
+					),
+				),
+				'expected_output' => '.wp-layout > :where(:not(.alignleft):not(.alignright):not(.alignfull)){max-width:var(--wp--style--global--content-size, none);}.wp-layout > .alignwide{max-width:var(--wp--style--global--wide-size, none);}.wp-layout .alignfull{max-width:none;}',
+			),
 			'constrained layout with block gap support'    => array(
 				'args'            => array(
 					'selector'              => '.wp-layout',