diff --git a/src/Internal/Silencer.php b/src/Internal/Silencer.php
new file mode 100644
index 00000000000..715e8fcd5f7
--- /dev/null
+++ b/src/Internal/Silencer.php
@@ -0,0 +1,41 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Internal;
+
+use Closure;
+use function restore_error_handler;
+use function set_error_handler;
+
+/**
+ * Runs something that predictably emits diagnostics which are none of the user's business, and keeps
+ * them to itself.
+ *
+ * Not the `@` operator, and not Composer's `Silencer` either: both work by lowering what is reported,
+ * and PHP calls a user error handler for a diagnostic regardless of `error_reporting()`. A handler that
+ * does not consult it therefore still sees everything `@` was meant to hide, and Xdebug's `scream`
+ * disables `@` outright. A handler of our own, on top of the stack for the duration of the call, is
+ * called instead of theirs and reports nothing - and theirs is back in place afterwards.
+ *
+ * Use it only where the diagnostics are expected and meaningless, never to hide a failure that should
+ * be handled: the callable's own return value still says whether it worked.
+ */
+final class Silencer
+{
+
+	/**
+	 * @template T
+	 * @param Closure(): T $callback
+	 * @return T
+	 */
+	public static function call(Closure $callback)
+	{
+		set_error_handler(static fn (): bool => true);
+
+		try {
+			return $callback();
+		} finally {
+			restore_error_handler();
+		}
+	}
+
+}
diff --git a/src/Type/Php/OpenSslCipherMethodsProvider.php b/src/Type/Php/OpenSslCipherMethodsProvider.php
index 056d9df9080..ccd6ab9401a 100644
--- a/src/Type/Php/OpenSslCipherMethodsProvider.php
+++ b/src/Type/Php/OpenSslCipherMethodsProvider.php
@@ -5,6 +5,7 @@
 use PHPStan\Analyser\DependencyTracker;
 use PHPStan\Analyser\ResultCache\ResultCacheValueExtension;
 use PHPStan\DependencyInjection\AutowiredService;
+use PHPStan\Internal\Silencer;
 use function array_filter;
 use function array_map;
 use function array_values;
@@ -54,10 +55,14 @@ private function getSupportedCipherMethods(): array
 			// openssl_get_cipher_methods() reports algorithms that are not actually
 			// supported on PHP 8.0-8.4 due to https://github.com/php/php-src/issues/19994
 			// Filter by actually testing each algorithm with openssl_cipher_iv_length().
-			$methods = array_values(array_filter(
+			//
+			// Probing an unsupported algorithm warns, and @ is not enough on its own: a user error
+			// handler that does not consult error_reporting() is still called for a suppressed
+			// diagnostic, and whatever installs one is out of our hands. See Silencer.
+			$methods = Silencer::call(static fn (): array => array_values(array_filter(
 				openssl_get_cipher_methods(true),
-				static fn (string $algorithm): bool => @openssl_cipher_iv_length($algorithm) !== false,
-			));
+				static fn (string $algorithm): bool => openssl_cipher_iv_length($algorithm) !== false,
+			)));
 		}
 
 		$this->supportedCipherMethods = array_map('strtolower', $methods);
diff --git a/tests/PHPStan/Type/Php/OpenSslCipherMethodsProviderTest.php b/tests/PHPStan/Type/Php/OpenSslCipherMethodsProviderTest.php
index 94b9f17093c..f06573acecc 100644
--- a/tests/PHPStan/Type/Php/OpenSslCipherMethodsProviderTest.php
+++ b/tests/PHPStan/Type/Php/OpenSslCipherMethodsProviderTest.php
@@ -6,6 +6,8 @@
 use PHPStan\Analyser\ScopeFactory;
 use PHPStan\Analyser\ValueDependencyCollector;
 use PHPStan\Testing\PHPStanTestCase;
+use function restore_error_handler;
+use function set_error_handler;
 
 class OpenSslCipherMethodsProviderTest extends PHPStanTestCase
 {
@@ -44,6 +46,36 @@ public function testIsSupportedCipherMethodTracksTheCipher(): void
 		], $dependencies['dependents']['/project/src/Analysed.php']['analysis']);
 	}
 
+	/**
+	 * Reading the ciphers out of the runtime means probing each one, and on PHP 8.0-8.4
+	 * openssl_get_cipher_methods() reports algorithms openssl_cipher_iv_length() rejects with a
+	 * warning (php/php-src#19994) - 40 of 248 on PHP 8.4.23. `@` does not settle that: a user error
+	 * handler that does not consult error_reporting() is still called for a suppressed diagnostic.
+	 * See phpstan/phpstan#15176.
+	 *
+	 * Vacuous on a PHP where nothing is rejected, which is why the count is not asserted - only that
+	 * whatever the probe does stays inside it.
+	 */
+	public function testProbingTheRuntimeLeaksNoWarningThroughAnUnsuppressedHandler(): void
+	{
+		$leaked = [];
+		set_error_handler(static function (int $errno, string $errstr) use (&$leaked): bool {
+			// deliberately does not check error_reporting(), so the @ operator does not hide anything
+			$leaked[] = $errstr;
+
+			return true;
+		});
+
+		try {
+			$value = (new OpenSslCipherMethodsProvider())->getValue('aes-128-cbc');
+		} finally {
+			restore_error_handler();
+		}
+
+		$this->assertSame([], $leaked, 'Probing the runtime for supported ciphers must not emit warnings.');
+		$this->assertContains($value, ['supported', 'unsupported']);
+	}
+
 	/**
 	 * @param list<string> $supportedCipherMethods
 	 */