diff --git a/src/wp-includes/block-patterns.php b/src/wp-includes/block-patterns.php
index dd70d2b589fd6..a1a7a67d818e2 100644
--- a/src/wp-includes/block-patterns.php
+++ b/src/wp-includes/block-patterns.php
@@ -350,9 +350,25 @@ function _register_theme_block_patterns() {
 				continue;
 			}
 
+			$file_path = $dirpath . $file;
+
+			if ( ! file_exists( $file_path ) ) {
+				_doing_it_wrong(
+					__FUNCTION__,
+					sprintf(
+						/* translators: %s: file name. */
+						__( 'Could not register file "%s" as a block pattern as the file does not exist.' ),
+						$file
+					),
+					'6.4.0'
+				);
+				$theme->delete_pattern_cache();
+				continue;
+			}
+
 			// The actual pattern content is the output of the file.
 			ob_start();
-			include $dirpath . $file;
+			include $file_path;
 			$pattern_data['content'] = ob_get_clean();
 			if ( ! $pattern_data['content'] ) {
 				continue;
@@ -408,11 +424,13 @@ function _register_theme_block_patterns() {
 function _wp_get_block_patterns( WP_Theme $theme ) {
 	$can_use_cached = ! wp_is_development_mode( 'theme' );
 
-	if ( $can_use_cached ) {
-		$pattern_data = $theme->get_pattern_cache();
-		if ( is_array( $pattern_data ) ) {
+	$pattern_data = $theme->get_pattern_cache();
+	if ( is_array( $pattern_data ) ) {
+		if ( $can_use_cached ) {
 			return $pattern_data;
 		}
+		// If in development mode, clear pattern cache.
+		$theme->delete_pattern_cache();
 	}
 
 	$dirpath      = $theme->get_stylesheet_directory() . '/patterns/';
diff --git a/tests/phpunit/tests/blocks/wpGetBlockPatterns.php b/tests/phpunit/tests/blocks/wpGetBlockPatterns.php
index aea0fbc6f16af..4e7f67612bb92 100644
--- a/tests/phpunit/tests/blocks/wpGetBlockPatterns.php
+++ b/tests/phpunit/tests/blocks/wpGetBlockPatterns.php
@@ -18,7 +18,6 @@ class Tests_Blocks_WpGetBlockPatterns extends WP_UnitTestCase {
 	 *
 	 * @param string $theme    The theme's slug.
 	 * @param array  $expected The expected pattern data.
-
 	 */
 	public function test_should_return_block_patterns( $theme, $expected ) {
 		$patterns = _wp_get_block_patterns( wp_get_theme( $theme ) );
@@ -118,4 +117,37 @@ public function data_wp_get_block_patterns() {
 			),
 		);
 	}
+
+	/**
+	 * Tests that _wp_get_block_patterns() clears existing transient when in theme development mode.
+	 *
+	 * @ticket 59591
+	 */
+	public function test_should_clear_existing_transient_when_in_development_mode() {
+		$theme = wp_get_theme( 'block-theme-patterns' );
+
+		// Calling the function should set the cache.
+		_wp_get_block_patterns( $theme );
+		$this->assertSameSets(
+			array(
+				'cta.php' => array(
+					'title'       => 'Centered Call To Action',
+					'slug'        => 'block-theme-patterns/cta',
+					'description' => '',
+					'categories'  => array( 'call-to-action' ),
+				),
+			),
+			$theme->get_pattern_cache(),
+			'The transient for block theme patterns should be set'
+		);
+
+		// Calling the function while in theme development mode should clear the cache.
+		$GLOBALS['_wp_tests_development_mode'] = 'theme';
+		_wp_get_block_patterns( $theme );
+		unset( $GLOBALS['_wp_tests_development_mode'] ); // Reset to not pollute other tests.
+		$this->assertFalse(
+			$theme->get_pattern_cache(),
+			'The transient for block theme patterns should have been cleared due to theme development mode'
+		);
+	}
 }