diff --git a/src/wp-includes/post.php b/src/wp-includes/post.php
index 3940519d4dc15..80be22202d522 100644
--- a/src/wp-includes/post.php
+++ b/src/wp-includes/post.php
@@ -2262,6 +2262,11 @@ function _add_post_type_submenus() {
  * A third, optional parameter can also be passed along with a feature to provide
  * additional information about supporting that feature.
  *
+ * When calling this function multiple times for the same post type and feature
+ * with associative array arguments, the arguments will be merged rather than
+ * overwritten. This allows multiple calls to add different sub-properties to
+ * the same feature.
+ *
  * Example usage:
  *
  *     add_post_type_support( 'my_post_type', 'comments' );
@@ -2275,6 +2280,8 @@ function _add_post_type_submenus() {
  * @since 3.0.0
  * @since 5.3.0 Formalized the existing and already documented `...$args` parameter
  *              by adding it to the function signature.
+ * @since 6.9.0 Multiple calls to add support for the same feature with associative
+ *              array arguments now merge the arguments instead of overwriting them.
  *
  * @global array $_wp_post_type_features
  *
@@ -2289,7 +2296,21 @@ function add_post_type_support( $post_type, $feature, ...$args ) {
 	$features = (array) $feature;
 	foreach ( $features as $feature ) {
 		if ( $args ) {
-			$_wp_post_type_features[ $post_type ][ $feature ] = $args;
+			// Check if feature already exists with args and if both are associative arrays that should be merged.
+			if (
+				isset( $_wp_post_type_features[ $post_type ][ $feature ][0] ) &&
+				is_array( $_wp_post_type_features[ $post_type ][ $feature ][0] ) &&
+				isset( $args[0] ) &&
+				is_array( $args[0] )
+			) {
+				// Merge the associative arrays to preserve existing properties.
+				$_wp_post_type_features[ $post_type ][ $feature ][0] = array_merge(
+					$_wp_post_type_features[ $post_type ][ $feature ][0],
+					$args[0]
+				);
+			} else {
+				$_wp_post_type_features[ $post_type ][ $feature ] = $args;
+			}
 		} else {
 			$_wp_post_type_features[ $post_type ][ $feature ] = true;
 		}
diff --git a/tests/phpunit/tests/post/types.php b/tests/phpunit/tests/post/types.php
index 96519586d6cff..cd5092cab5e7e 100644
--- a/tests/phpunit/tests/post/types.php
+++ b/tests/phpunit/tests/post/types.php
@@ -215,6 +215,231 @@ public function test_post_type_supports() {
 		$this->assertFalse( post_type_supports( 'notaposttype', 'notafeature' ) );
 	}
 
+	/**
+	 * Tests that add_post_type_support() merges array arguments on subsequent calls.
+	 *
+	 * @ticket 64156
+	 */
+	public function test_add_post_type_support_merges_array_arguments() {
+		register_post_type( 'foo' );
+
+		// First call with array arguments.
+		add_post_type_support(
+			'foo',
+			'editor',
+			array(
+				'default-mode' => 'template-locked',
+			)
+		);
+
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertIsArray( $support['editor'] );
+		$this->assertArrayHasKey( 0, $support['editor'] );
+		$this->assertIsArray( $support['editor'][0] );
+		$this->assertSame( 'template-locked', $support['editor'][0]['default-mode'] );
+
+		// Second call with different array arguments should merge.
+		add_post_type_support(
+			'foo',
+			'editor',
+			array(
+				'block-comments' => true,
+			)
+		);
+
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertIsArray( $support['editor'] );
+		$this->assertArrayHasKey( 0, $support['editor'] );
+		$this->assertIsArray( $support['editor'][0] );
+		$this->assertSame( 'template-locked', $support['editor'][0]['default-mode'] );
+		$this->assertTrue( $support['editor'][0]['block-comments'] );
+
+		// Third call with yet another property should merge with both previous.
+		add_post_type_support(
+			'foo',
+			'editor',
+			array(
+				'another-option' => 'test-value',
+			)
+		);
+
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertSame( 'template-locked', $support['editor'][0]['default-mode'] );
+		$this->assertTrue( $support['editor'][0]['block-comments'] );
+		$this->assertSame( 'test-value', $support['editor'][0]['another-option'] );
+
+		_unregister_post_type( 'foo' );
+	}
+
+	/**
+	 * Tests that add_post_type_support() overwrites values when called with the same key.
+	 *
+	 * @ticket 64156
+	 */
+	public function test_add_post_type_support_overwrites_same_key() {
+		register_post_type( 'foo' );
+
+		add_post_type_support(
+			'foo',
+			'editor',
+			array(
+				'default-mode' => 'template-locked',
+			)
+		);
+
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertSame( 'template-locked', $support['editor'][0]['default-mode'] );
+
+		// Calling with same key but different value should overwrite.
+		add_post_type_support(
+			'foo',
+			'editor',
+			array(
+				'default-mode' => 'unlocked',
+			)
+		);
+
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertSame( 'unlocked', $support['editor'][0]['default-mode'] );
+
+		_unregister_post_type( 'foo' );
+	}
+
+	/**
+	 * Tests backwards compatibility: calling add_post_type_support() without args still works.
+	 *
+	 * @ticket 64156
+	 */
+	public function test_add_post_type_support_without_args() {
+		register_post_type( 'foo' );
+
+		add_post_type_support( 'foo', 'custom-fields' );
+
+		$this->assertTrue( post_type_supports( 'foo', 'custom-fields' ) );
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertTrue( $support['custom-fields'] );
+
+		_unregister_post_type( 'foo' );
+	}
+
+	/**
+	 * Tests backwards compatibility: calling add_post_type_support() with args after
+	 * setting it to true should overwrite with args.
+	 *
+	 * @ticket 64156
+	 */
+	public function test_add_post_type_support_with_args_after_true() {
+		register_post_type( 'foo' );
+
+		// First call without args sets to true.
+		add_post_type_support( 'foo', 'editor' );
+
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertTrue( $support['editor'] );
+
+		// Second call with args should overwrite true with args.
+		add_post_type_support(
+			'foo',
+			'editor',
+			array(
+				'default-mode' => 'template-locked',
+			)
+		);
+
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertIsArray( $support['editor'] );
+		$this->assertSame( 'template-locked', $support['editor'][0]['default-mode'] );
+
+		_unregister_post_type( 'foo' );
+	}
+
+	/**
+	 * Tests backwards compatibility: calling add_post_type_support() without args after
+	 * setting it with args should overwrite with true.
+	 *
+	 * @ticket 64156
+	 */
+	public function test_add_post_type_support_without_args_after_array() {
+		register_post_type( 'foo' );
+
+		// First call with args.
+		add_post_type_support(
+			'foo',
+			'editor',
+			array(
+				'default-mode' => 'template-locked',
+			)
+		);
+
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertIsArray( $support['editor'] );
+		$this->assertSame( 'template-locked', $support['editor'][0]['default-mode'] );
+
+		// Second call without args should overwrite args with true.
+		add_post_type_support( 'foo', 'editor' );
+
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertTrue( $support['editor'] );
+
+		_unregister_post_type( 'foo' );
+	}
+
+	/**
+	 * Tests that add_post_type_support() can add multiple features at once.
+	 *
+	 * @ticket 64156
+	 */
+	public function test_add_post_type_support_multiple_features() {
+		register_post_type( 'foo' );
+
+		add_post_type_support( 'foo', array( 'title', 'editor', 'thumbnail' ) );
+
+		$this->assertTrue( post_type_supports( 'foo', 'title' ) );
+		$this->assertTrue( post_type_supports( 'foo', 'editor' ) );
+		$this->assertTrue( post_type_supports( 'foo', 'thumbnail' ) );
+
+		_unregister_post_type( 'foo' );
+	}
+
+	/**
+	 * Tests that add_post_type_support() works with nested array arguments.
+	 *
+	 * @ticket 64156
+	 */
+	public function test_add_post_type_support_with_nested_arrays() {
+		register_post_type( 'foo' );
+
+		add_post_type_support(
+			'foo',
+			'editor',
+			array(
+				'allowed_blocks' => array( 'core/paragraph', 'core/heading' ),
+			)
+		);
+
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertIsArray( $support['editor'][0]['allowed_blocks'] );
+		$this->assertContains( 'core/paragraph', $support['editor'][0]['allowed_blocks'] );
+		$this->assertContains( 'core/heading', $support['editor'][0]['allowed_blocks'] );
+
+		// Adding another nested array should merge.
+		add_post_type_support(
+			'foo',
+			'editor',
+			array(
+				'disallowed_blocks' => array( 'core/code' ),
+			)
+		);
+
+		$support = get_all_post_type_supports( 'foo' );
+		$this->assertIsArray( $support['editor'][0]['allowed_blocks'] );
+		$this->assertIsArray( $support['editor'][0]['disallowed_blocks'] );
+		$this->assertContains( 'core/paragraph', $support['editor'][0]['allowed_blocks'] );
+		$this->assertContains( 'core/code', $support['editor'][0]['disallowed_blocks'] );
+
+		_unregister_post_type( 'foo' );
+	}
+
 	/**
 	 * @ticket 21586
 	 * @ticket 41172