diff --git a/src/wp-includes/class-wp-scripts.php b/src/wp-includes/class-wp-scripts.php
index e627f28eb4fbb..02b925578f052 100644
--- a/src/wp-includes/class-wp-scripts.php
+++ b/src/wp-includes/class-wp-scripts.php
@@ -871,6 +871,18 @@ private function get_dependents( $handle ) {
 		return $dependents;
 	}
 
+	/**
+	 * Determines if a script loading strategy is valid.
+	 *
+	 * @param string $strategy A script loading strategy.
+	 * @return bool True if the strategy is of an allowed type, false otherwise.
+	 */
+	private function is_valid_strategy( $strategy ) {
+		$allowed_strategies = array( 'blocking', 'defer', 'async' );
+
+		return in_array( $strategy, $allowed_strategies, true );
+	}
+
 	/**
 	 * Get the strategy assigned during script registration.
 	 *
@@ -879,8 +891,24 @@ private function get_dependents( $handle ) {
 	 */
 	private function get_intended_strategy( $handle ) {
 		$script_args = $this->get_data( $handle, 'script_args' );
+		$strategy    = isset( $script_args['strategy'] ) ? $script_args['strategy'] : false;
+
+		if ( $strategy && ! $this->is_valid_strategy( $strategy ) ) {
+			_doing_it_wrong(
+				__METHOD__,
+				sprintf(
+					/* translators: 1: $strategy, 2: $handle */
+					__( 'Invalid strategy `%1$s` defined for `%2$s` during script registration.' ),
+					$strategy,
+					$handle
+				),
+				'6.3.0'
+			);
+
+			return false;
+		}
 
-		return isset( $script_args['strategy'] ) ? $script_args['strategy'] : false;
+		return $strategy;
 	}
 
 	/**
diff --git a/tests/phpunit/tests/dependencies/scripts.php b/tests/phpunit/tests/dependencies/scripts.php
index 6b267c9623d99..7670f0bb37096 100644
--- a/tests/phpunit/tests/dependencies/scripts.php
+++ b/tests/phpunit/tests/dependencies/scripts.php
@@ -628,6 +628,26 @@ public function test_get_normalized_script_args() {
 		$this->assertSame( $expected_args, $wp_scripts->get_data( 'footer-old', 'script_args' ) );
 	}
 
+	/**
+	 * Test script strategy doing it wrong.
+	 *
+	 * For an invalid strategy defined during script registration, default to a blocking strategy.
+	 *
+	 * @ticket 12009
+	 */
+	public function test_script_strategy_doing_it_wrong() {
+		$this->setExpectedIncorrectUsage( 'WP_Scripts::get_intended_strategy' );
+
+		wp_register_script( 'invalid-strategy', '/defaults.js', array(), null, array( 'strategy' => 'random-strategy' ) );
+		wp_enqueue_script( 'invalid-strategy' );
+
+		$output = get_echo( 'wp_print_scripts' );
+
+		$expected = "<script type='text/javascript' src='/defaults.js' id='invalid-strategy-js'></script>\n";
+
+		$this->assertSame( $expected, $output );
+	}
+
 	/**
 	 * Test script concatenation with deferred main script.
 	 *